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 * Copyright (c) 1995, 2016, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package java.net;

import sun.security.util.SecurityConstants;

import java.io.InputStream;
import java.io.OutputStream;
import java.io.IOException;
import java.nio.channels.SocketChannel;
import java.security.AccessController;
import java.security.PrivilegedExceptionAction;
import java.security.PrivilegedAction;
import java.util.Set;
import java.util.Collections;

This class implements client sockets (also called just
"sockets"). A socket is an endpoint for communication
between two machines.
 The actual work of the socket is performed by an instance of the SocketImpl class. An application, by changing the socket factory that creates the socket implementation, can configure itself to create sockets appropriate to the local firewall. 
Author:
 unascribed
See Also:
setSocketImplFactory(SocketImplFactory)
SocketImpl
SocketChannel
Since:
  1.0/**
 * This class implements client sockets (also called just
 * "sockets"). A socket is an endpoint for communication
 * between two machines.
 * <p>
 * The actual work of the socket is performed by an instance of the
 * {@code SocketImpl} class. An application, by changing
 * the socket factory that creates the socket implementation,
 * can configure itself to create sockets appropriate to the local
 * firewall.
 *
 * @author  unascribed
 * @see     java.net.Socket#setSocketImplFactory(java.net.SocketImplFactory)
 * @see     java.net.SocketImpl
 * @see     java.nio.channels.SocketChannel
 * @since   1.0
 */
public
class Socket implements java.io.Closeable {
    
Various states of this socket.
/**
     * Various states of this socket.
     */
    private boolean created = false;
    private boolean bound = false;
    private boolean connected = false;
    private boolean closed = false;
    private Object closeLock = new Object();
    private boolean shutIn = false;
    private boolean shutOut = false;

    
The implementation of this Socket.
/**
     * The implementation of this Socket.
     */
    SocketImpl impl;

    
Are we using an older SocketImpl?
/**
     * Are we using an older SocketImpl?
     */
    private boolean oldImpl = false;

    
Creates an unconnected socket, with the
system-default type of SocketImpl.
Since:
  1.1
@revised
1.4/**
     * Creates an unconnected socket, with the
     * system-default type of SocketImpl.
     *
     * @since   1.1
     * @revised 1.4
     */
    public Socket() {
        setImpl();
    }

    
Creates an unconnected socket, specifying the type of proxy, if any,
that should be used regardless of any other settings.
 If there is a security manager, its checkConnect method is called with the proxy host address and port number as its arguments. This could result in a SecurityException. 

Examples:
 
Socket s = new Socket(Proxy.NO_PROXY); will create a plain socket ignoring any other proxy configuration.
Socket s = new Socket(new Proxy(Proxy.Type.SOCKS, new InetSocketAddress("socks.mydom.com", 1080))); will create a socket connecting through the specified SOCKS proxy server.

Params:
proxy – a Proxy object specifying what kind of proxying should be used.
Throws:
IllegalArgumentException – if the proxy is of an invalid type or null.
SecurityException – if a security manager is present and
                          permission to connect to the proxy is
                          denied.
See Also:
ProxySelector
Proxy
Since:
  1.5/**
     * Creates an unconnected socket, specifying the type of proxy, if any,
     * that should be used regardless of any other settings.
     * <P>
     * If there is a security manager, its {@code checkConnect} method
     * is called with the proxy host address and port number
     * as its arguments. This could result in a SecurityException.
     * <P>
     * Examples:
     * <UL> <LI>{@code Socket s = new Socket(Proxy.NO_PROXY);} will create
     * a plain socket ignoring any other proxy configuration.</LI>
     * <LI>{@code Socket s = new Socket(new Proxy(Proxy.Type.SOCKS, new InetSocketAddress("socks.mydom.com", 1080)));}
     * will create a socket connecting through the specified SOCKS proxy
     * server.</LI>
     * </UL>
     *
     * @param proxy a {@link java.net.Proxy Proxy} object specifying what kind
     *              of proxying should be used.
     * @throws IllegalArgumentException if the proxy is of an invalid type
     *          or {@code null}.
     * @throws SecurityException if a security manager is present and
     *                           permission to connect to the proxy is
     *                           denied.
     * @see java.net.ProxySelector
     * @see java.net.Proxy
     *
     * @since   1.5
     */
    public Socket(Proxy proxy) {
        // Create a copy of Proxy as a security measure
        if (proxy == null) {
            throw new IllegalArgumentException("Invalid Proxy");
        }
        Proxy p = proxy == Proxy.NO_PROXY ? Proxy.NO_PROXY
                                          : sun.net.ApplicationProxy.create(proxy);
        Proxy.Type type = p.type();
        if (type == Proxy.Type.SOCKS || type == Proxy.Type.HTTP) {
            SecurityManager security = System.getSecurityManager();
            InetSocketAddress epoint = (InetSocketAddress) p.address();
            if (epoint.getAddress() != null) {
                checkAddress (epoint.getAddress(), "Socket");
            }
            if (security != null) {
                if (epoint.isUnresolved())
                    epoint = new InetSocketAddress(epoint.getHostName(), epoint.getPort());
                if (epoint.isUnresolved())
                    security.checkConnect(epoint.getHostName(), epoint.getPort());
                else
                    security.checkConnect(epoint.getAddress().getHostAddress(),
                                  epoint.getPort());
            }
            impl = type == Proxy.Type.SOCKS ? new SocksSocketImpl(p)
                                            : new HttpConnectSocketImpl(p);
            impl.setSocket(this);
        } else {
            if (p == Proxy.NO_PROXY) {
                if (factory == null) {
                    impl = new PlainSocketImpl();
                    impl.setSocket(this);
                } else
                    setImpl();
            } else
                throw new IllegalArgumentException("Invalid Proxy");
        }
    }

    
Creates an unconnected Socket with a user-specified
SocketImpl.
Params:
impl – an instance of a SocketImpl
the subclass wishes to use on the Socket.
Throws:
SocketException – if there is an error in the underlying protocol,
such as a TCP error.
SecurityException – if impl is non-null and a security manager is set and its checkPermission method doesn't allow NetPermission("setSocketImpl").
Since:
  1.1/**
     * Creates an unconnected Socket with a user-specified
     * SocketImpl.
     *
     * @param impl an instance of a <B>SocketImpl</B>
     * the subclass wishes to use on the Socket.
     *
     * @exception SocketException if there is an error in the underlying protocol,
     * such as a TCP error.
     *
     * @throws SecurityException if {@code impl} is non-null and a security manager is set
     * and its {@code checkPermission} method doesn't allow {@code NetPermission("setSocketImpl")}.
     *
     * @since   1.1
     */
    protected Socket(SocketImpl impl) throws SocketException {
        checkPermission(impl);
        this.impl = impl;
        if (impl != null) {
            checkOldImpl();
            this.impl.setSocket(this);
        }
    }

    private static Void checkPermission(SocketImpl impl) {
        if (impl == null) {
            return null;
        }
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) {
            sm.checkPermission(SecurityConstants.SET_SOCKETIMPL_PERMISSION);
        }
        return null;
    }

    
Creates a stream socket and connects it to the specified port
number on the named host.
 If the specified host is null it is the equivalent of specifying the address as InetAddress.getByName(null). In other words, it is equivalent to specifying an address of the loopback interface. 
 If the application has specified a server socket factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a "plain" socket is created. 
 If there is a security manager, its checkConnect method is called with the host address and port as its arguments. This could result in a SecurityException. 
Params:
host –  the host name, or null for the loopback address.
port –   the port number.
Throws:
UnknownHostException – if the IP address of
the host could not be determined.
IOException –  if an I/O error occurs when creating the socket.
SecurityException –  if a security manager exists and its checkConnect method doesn't allow the operation.
IllegalArgumentException – if the port parameter is outside
            the specified range of valid port values, which is between
            0 and 65535, inclusive.
See Also:
setSocketImplFactory(SocketImplFactory)
SocketImpl
SocketImplFactory.createSocketImpl()
SecurityManager.checkConnect/**
     * Creates a stream socket and connects it to the specified port
     * number on the named host.
     * <p>
     * If the specified host is {@code null} it is the equivalent of
     * specifying the address as
     * {@link java.net.InetAddress#getByName InetAddress.getByName}{@code (null)}.
     * In other words, it is equivalent to specifying an address of the
     * loopback interface. </p>
     * <p>
     * If the application has specified a server socket factory, that
     * factory's {@code createSocketImpl} method is called to create
     * the actual socket implementation. Otherwise a "plain" socket is created.
     * <p>
     * If there is a security manager, its
     * {@code checkConnect} method is called
     * with the host address and {@code port}
     * as its arguments. This could result in a SecurityException.
     *
     * @param      host   the host name, or {@code null} for the loopback address.
     * @param      port   the port number.
     *
     * @exception  UnknownHostException if the IP address of
     * the host could not be determined.
     *
     * @exception  IOException  if an I/O error occurs when creating the socket.
     * @exception  SecurityException  if a security manager exists and its
     *             {@code checkConnect} method doesn't allow the operation.
     * @exception  IllegalArgumentException if the port parameter is outside
     *             the specified range of valid port values, which is between
     *             0 and 65535, inclusive.
     * @see        java.net.Socket#setSocketImplFactory(java.net.SocketImplFactory)
     * @see        java.net.SocketImpl
     * @see        java.net.SocketImplFactory#createSocketImpl()
     * @see        SecurityManager#checkConnect
     */
    public Socket(String host, int port)
        throws UnknownHostException, IOException
    {
        this(host != null ? new InetSocketAddress(host, port) :
             new InetSocketAddress(InetAddress.getByName(null), port),
             (SocketAddress) null, true);
    }

    
Creates a stream socket and connects it to the specified port
number at the specified IP address.
 If the application has specified a socket factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a "plain" socket is created. 
 If there is a security manager, its checkConnect method is called with the host address and port as its arguments. This could result in a SecurityException. 
Params:
address –   the IP address.
port –      the port number.
Throws:
IOException –  if an I/O error occurs when creating the socket.
SecurityException –  if a security manager exists and its checkConnect method doesn't allow the operation.
IllegalArgumentException – if the port parameter is outside
            the specified range of valid port values, which is between
            0 and 65535, inclusive.
NullPointerException – if address is null.
See Also:
setSocketImplFactory(SocketImplFactory)
SocketImpl
SocketImplFactory.createSocketImpl()
SecurityManager.checkConnect/**
     * Creates a stream socket and connects it to the specified port
     * number at the specified IP address.
     * <p>
     * If the application has specified a socket factory, that factory's
     * {@code createSocketImpl} method is called to create the
     * actual socket implementation. Otherwise a "plain" socket is created.
     * <p>
     * If there is a security manager, its
     * {@code checkConnect} method is called
     * with the host address and {@code port}
     * as its arguments. This could result in a SecurityException.
     *
     * @param      address   the IP address.
     * @param      port      the port number.
     * @exception  IOException  if an I/O error occurs when creating the socket.
     * @exception  SecurityException  if a security manager exists and its
     *             {@code checkConnect} method doesn't allow the operation.
     * @exception  IllegalArgumentException if the port parameter is outside
     *             the specified range of valid port values, which is between
     *             0 and 65535, inclusive.
     * @exception  NullPointerException if {@code address} is null.
     * @see        java.net.Socket#setSocketImplFactory(java.net.SocketImplFactory)
     * @see        java.net.SocketImpl
     * @see        java.net.SocketImplFactory#createSocketImpl()
     * @see        SecurityManager#checkConnect
     */
    public Socket(InetAddress address, int port) throws IOException {
        this(address != null ? new InetSocketAddress(address, port) : null,
             (SocketAddress) null, true);
    }

    
Creates a socket and connects it to the specified remote host on
the specified remote port. The Socket will also bind() to the local
address and port supplied.
 If the specified host is null it is the equivalent of specifying the address as InetAddress.getByName(null). In other words, it is equivalent to specifying an address of the loopback interface. 
 A local port number of zero will let the system pick up a free port in the bind operation.
 If there is a security manager, its checkConnect method is called with the host address and port as its arguments. This could result in a SecurityException. 
Params:
host – the name of the remote host, or null for the loopback address.
port – the remote port
localAddr – the local address the socket is bound to, or null for the anyLocal address.
localPort – the local port the socket is bound to, or zero for a system selected free port.
Throws:
IOException –  if an I/O error occurs when creating the socket.
SecurityException –  if a security manager exists and its checkConnect method doesn't allow the connection to the destination, or if its checkListen method doesn't allow the bind to the local port.
IllegalArgumentException – if the port parameter or localPort
            parameter is outside the specified range of valid port values,
            which is between 0 and 65535, inclusive.
See Also:
SecurityManager.checkConnect
Since:
  1.1/**
     * Creates a socket and connects it to the specified remote host on
     * the specified remote port. The Socket will also bind() to the local
     * address and port supplied.
     * <p>
     * If the specified host is {@code null} it is the equivalent of
     * specifying the address as
     * {@link java.net.InetAddress#getByName InetAddress.getByName}{@code (null)}.
     * In other words, it is equivalent to specifying an address of the
     * loopback interface. </p>
     * <p>
     * A local port number of {@code zero} will let the system pick up a
     * free port in the {@code bind} operation.</p>
     * <p>
     * If there is a security manager, its
     * {@code checkConnect} method is called
     * with the host address and {@code port}
     * as its arguments. This could result in a SecurityException.
     *
     * @param host the name of the remote host, or {@code null} for the loopback address.
     * @param port the remote port
     * @param localAddr the local address the socket is bound to, or
     *        {@code null} for the {@code anyLocal} address.
     * @param localPort the local port the socket is bound to, or
     *        {@code zero} for a system selected free port.
     * @exception  IOException  if an I/O error occurs when creating the socket.
     * @exception  SecurityException  if a security manager exists and its
     *             {@code checkConnect} method doesn't allow the connection
     *             to the destination, or if its {@code checkListen} method
     *             doesn't allow the bind to the local port.
     * @exception  IllegalArgumentException if the port parameter or localPort
     *             parameter is outside the specified range of valid port values,
     *             which is between 0 and 65535, inclusive.
     * @see        SecurityManager#checkConnect
     * @since   1.1
     */
    public Socket(String host, int port, InetAddress localAddr,
                  int localPort) throws IOException {
        this(host != null ? new InetSocketAddress(host, port) :
               new InetSocketAddress(InetAddress.getByName(null), port),
             new InetSocketAddress(localAddr, localPort), true);
    }

    
Creates a socket and connects it to the specified remote address on
the specified remote port. The Socket will also bind() to the local
address and port supplied.
 If the specified local address is null it is the equivalent of specifying the address as the AnyLocal address (see InetAddress.isAnyLocalAddress()). 
 A local port number of zero will let the system pick up a free port in the bind operation.
 If there is a security manager, its checkConnect method is called with the host address and port as its arguments. This could result in a SecurityException. 
Params:
address – the remote address
port – the remote port
localAddr – the local address the socket is bound to, or null for the anyLocal address.
localPort – the local port the socket is bound to or zero for a system selected free port.
Throws:
IOException –  if an I/O error occurs when creating the socket.
SecurityException –  if a security manager exists and its checkConnect method doesn't allow the connection to the destination, or if its checkListen method doesn't allow the bind to the local port.
IllegalArgumentException – if the port parameter or localPort
            parameter is outside the specified range of valid port values,
            which is between 0 and 65535, inclusive.
NullPointerException – if address is null.
See Also:
SecurityManager.checkConnect
Since:
  1.1/**
     * Creates a socket and connects it to the specified remote address on
     * the specified remote port. The Socket will also bind() to the local
     * address and port supplied.
     * <p>
     * If the specified local address is {@code null} it is the equivalent of
     * specifying the address as the AnyLocal address
     * (see {@link java.net.InetAddress#isAnyLocalAddress InetAddress.isAnyLocalAddress}{@code ()}).
     * <p>
     * A local port number of {@code zero} will let the system pick up a
     * free port in the {@code bind} operation.</p>
     * <p>
     * If there is a security manager, its
     * {@code checkConnect} method is called
     * with the host address and {@code port}
     * as its arguments. This could result in a SecurityException.
     *
     * @param address the remote address
     * @param port the remote port
     * @param localAddr the local address the socket is bound to, or
     *        {@code null} for the {@code anyLocal} address.
     * @param localPort the local port the socket is bound to or
     *        {@code zero} for a system selected free port.
     * @exception  IOException  if an I/O error occurs when creating the socket.
     * @exception  SecurityException  if a security manager exists and its
     *             {@code checkConnect} method doesn't allow the connection
     *             to the destination, or if its {@code checkListen} method
     *             doesn't allow the bind to the local port.
     * @exception  IllegalArgumentException if the port parameter or localPort
     *             parameter is outside the specified range of valid port values,
     *             which is between 0 and 65535, inclusive.
     * @exception  NullPointerException if {@code address} is null.
     * @see        SecurityManager#checkConnect
     * @since   1.1
     */
    public Socket(InetAddress address, int port, InetAddress localAddr,
                  int localPort) throws IOException {
        this(address != null ? new InetSocketAddress(address, port) : null,
             new InetSocketAddress(localAddr, localPort), true);
    }

    
Creates a stream socket and connects it to the specified port
number on the named host.
 If the specified host is null it is the equivalent of specifying the address as InetAddress.getByName(null). In other words, it is equivalent to specifying an address of the loopback interface. 
 If the stream argument is true, this creates a stream socket. If the stream argument is false, it creates a datagram socket. 
 If the application has specified a server socket factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a "plain" socket is created. 
 If there is a security manager, its checkConnect method is called with the host address and port as its arguments. This could result in a SecurityException. 

If a UDP socket is used, TCP/IP related socket options will not apply.
Params:
host –  the host name, or null for the loopback address.
port –     the port number.
stream –  a boolean indicating whether this is a stream socket or a datagram socket.
Throws:
IOException –  if an I/O error occurs when creating the socket.
SecurityException –  if a security manager exists and its checkConnect method doesn't allow the operation.
IllegalArgumentException – if the port parameter is outside
            the specified range of valid port values, which is between
            0 and 65535, inclusive.
See Also:
setSocketImplFactory(SocketImplFactory)
SocketImpl
SocketImplFactory.createSocketImpl()
SecurityManager.checkConnect
Deprecated:
Use DatagramSocket instead for UDP transport./**
     * Creates a stream socket and connects it to the specified port
     * number on the named host.
     * <p>
     * If the specified host is {@code null} it is the equivalent of
     * specifying the address as
     * {@link java.net.InetAddress#getByName InetAddress.getByName}{@code (null)}.
     * In other words, it is equivalent to specifying an address of the
     * loopback interface. </p>
     * <p>
     * If the stream argument is {@code true}, this creates a
     * stream socket. If the stream argument is {@code false}, it
     * creates a datagram socket.
     * <p>
     * If the application has specified a server socket factory, that
     * factory's {@code createSocketImpl} method is called to create
     * the actual socket implementation. Otherwise a "plain" socket is created.
     * <p>
     * If there is a security manager, its
     * {@code checkConnect} method is called
     * with the host address and {@code port}
     * as its arguments. This could result in a SecurityException.
     * <p>
     * If a UDP socket is used, TCP/IP related socket options will not apply.
     *
     * @param      host     the host name, or {@code null} for the loopback address.
     * @param      port     the port number.
     * @param      stream   a {@code boolean} indicating whether this is
     *                      a stream socket or a datagram socket.
     * @exception  IOException  if an I/O error occurs when creating the socket.
     * @exception  SecurityException  if a security manager exists and its
     *             {@code checkConnect} method doesn't allow the operation.
     * @exception  IllegalArgumentException if the port parameter is outside
     *             the specified range of valid port values, which is between
     *             0 and 65535, inclusive.
     * @see        java.net.Socket#setSocketImplFactory(java.net.SocketImplFactory)
     * @see        java.net.SocketImpl
     * @see        java.net.SocketImplFactory#createSocketImpl()
     * @see        SecurityManager#checkConnect
     * @deprecated Use DatagramSocket instead for UDP transport.
     */
    @Deprecated
    public Socket(String host, int port, boolean stream) throws IOException {
        this(host != null ? new InetSocketAddress(host, port) :
               new InetSocketAddress(InetAddress.getByName(null), port),
             (SocketAddress) null, stream);
    }

    
Creates a socket and connects it to the specified port number at
the specified IP address.
 If the stream argument is true, this creates a stream socket. If the stream argument is false, it creates a datagram socket. 
 If the application has specified a server socket factory, that factory's createSocketImpl method is called to create the actual socket implementation. Otherwise a "plain" socket is created. 
If there is a security manager, its checkConnect method is called with host.getHostAddress() and port as its arguments. This could result in a SecurityException. 

If UDP socket is used, TCP/IP related socket options will not apply.
Params:
host –     the IP address.
port –      the port number.
stream –  if true, create a stream socket; otherwise, create a datagram socket.
Throws:
IOException –  if an I/O error occurs when creating the socket.
SecurityException –  if a security manager exists and its checkConnect method doesn't allow the operation.
IllegalArgumentException – if the port parameter is outside
            the specified range of valid port values, which is between
            0 and 65535, inclusive.
NullPointerException – if host is null.
See Also:
setSocketImplFactory(SocketImplFactory)
SocketImpl
SocketImplFactory.createSocketImpl()
SecurityManager.checkConnect
Deprecated:
Use DatagramSocket instead for UDP transport./**
     * Creates a socket and connects it to the specified port number at
     * the specified IP address.
     * <p>
     * If the stream argument is {@code true}, this creates a
     * stream socket. If the stream argument is {@code false}, it
     * creates a datagram socket.
     * <p>
     * If the application has specified a server socket factory, that
     * factory's {@code createSocketImpl} method is called to create
     * the actual socket implementation. Otherwise a "plain" socket is created.
     *
     * <p>If there is a security manager, its
     * {@code checkConnect} method is called
     * with {@code host.getHostAddress()} and {@code port}
     * as its arguments. This could result in a SecurityException.
     * <p>
     * If UDP socket is used, TCP/IP related socket options will not apply.
     *
     * @param      host     the IP address.
     * @param      port      the port number.
     * @param      stream    if {@code true}, create a stream socket;
     *                       otherwise, create a datagram socket.
     * @exception  IOException  if an I/O error occurs when creating the socket.
     * @exception  SecurityException  if a security manager exists and its
     *             {@code checkConnect} method doesn't allow the operation.
     * @exception  IllegalArgumentException if the port parameter is outside
     *             the specified range of valid port values, which is between
     *             0 and 65535, inclusive.
     * @exception  NullPointerException if {@code host} is null.
     * @see        java.net.Socket#setSocketImplFactory(java.net.SocketImplFactory)
     * @see        java.net.SocketImpl
     * @see        java.net.SocketImplFactory#createSocketImpl()
     * @see        SecurityManager#checkConnect
     * @deprecated Use DatagramSocket instead for UDP transport.
     */
    @Deprecated
    public Socket(InetAddress host, int port, boolean stream) throws IOException {
        this(host != null ? new InetSocketAddress(host, port) : null,
             new InetSocketAddress(0), stream);
    }

    private Socket(SocketAddress address, SocketAddress localAddr,
                   boolean stream) throws IOException {
        setImpl();

        // backward compatibility
        if (address == null)
            throw new NullPointerException();

        try {
            createImpl(stream);
            if (localAddr != null)
                bind(localAddr);
            connect(address);
        } catch (IOException | IllegalArgumentException | SecurityException e) {
            try {
                close();
            } catch (IOException ce) {
                e.addSuppressed(ce);
            }
            throw e;
        }
    }

    
Creates the socket implementation.
Params:
stream – a boolean value : true for a TCP socket, false for UDP.
Throws:
IOException – if creation fails
Since:
1.4/**
     * Creates the socket implementation.
     *
     * @param stream a {@code boolean} value : {@code true} for a TCP socket,
     *               {@code false} for UDP.
     * @throws IOException if creation fails
     * @since 1.4
     */
     void createImpl(boolean stream) throws SocketException {
        if (impl == null)
            setImpl();
        try {
            impl.create(stream);
            created = true;
        } catch (IOException e) {
            throw new SocketException(e.getMessage());
        }
    }

    private void checkOldImpl() {
        if (impl == null)
            return;
        // SocketImpl.connect() is a protected method, therefore we need to use
        // getDeclaredMethod, therefore we need permission to access the member

        oldImpl = AccessController.doPrivileged
                                (new PrivilegedAction<>() {
            public Boolean run() {
                Class<?> clazz = impl.getClass();
                while (true) {
                    try {
                        clazz.getDeclaredMethod("connect", SocketAddress.class, int.class);
                        return Boolean.FALSE;
                    } catch (NoSuchMethodException e) {
                        clazz = clazz.getSuperclass();
                        // java.net.SocketImpl class will always have this abstract method.
                        // If we have not found it by now in the hierarchy then it does not
                        // exist, we are an old style impl.
                        if (clazz.equals(java.net.SocketImpl.class)) {
                            return Boolean.TRUE;
                        }
                    }
                }
            }
        });
    }

    
Sets impl to the system-default type of SocketImpl.
Since:
1.4/**
     * Sets impl to the system-default type of SocketImpl.
     * @since 1.4
     */
    void setImpl() {
        if (factory != null) {
            impl = factory.createSocketImpl();
            checkOldImpl();
        } else {
            // No need to do a checkOldImpl() here, we know it's an up to date
            // SocketImpl!
            impl = new SocksSocketImpl();
        }
        if (impl != null)
            impl.setSocket(this);
    }


    
Get the SocketImpl attached to this socket, creating it if necessary. 
Throws:
SocketException – if creation fails
Returns:
 the SocketImpl attached to that ServerSocket.
Since:
1.4/**
     * Get the {@code SocketImpl} attached to this socket, creating
     * it if necessary.
     *
     * @return  the {@code SocketImpl} attached to that ServerSocket.
     * @throws SocketException if creation fails
     * @since 1.4
     */
    SocketImpl getImpl() throws SocketException {
        if (!created)
            createImpl(true);
        return impl;
    }

    
Connects this socket to the server.
Params:
endpoint – the SocketAddress
Throws:
IOException – if an error occurs during the connection
IllegalBlockingModeException – 
         if this socket has an associated channel,
         and the channel is in non-blocking mode
IllegalArgumentException – if endpoint is null or is a
         SocketAddress subclass not supported by this socket
Since:
1.4
@spec
JSR-51/**
     * Connects this socket to the server.
     *
     * @param   endpoint the {@code SocketAddress}
     * @throws  IOException if an error occurs during the connection
     * @throws  java.nio.channels.IllegalBlockingModeException
     *          if this socket has an associated channel,
     *          and the channel is in non-blocking mode
     * @throws  IllegalArgumentException if endpoint is null or is a
     *          SocketAddress subclass not supported by this socket
     * @since 1.4
     * @spec JSR-51
     */
    public void connect(SocketAddress endpoint) throws IOException {
        connect(endpoint, 0);
    }

    
Connects this socket to the server with a specified timeout value.
A timeout of zero is interpreted as an infinite timeout. The connection
will then block until established or an error occurs.
Params:
endpoint – the SocketAddress
timeout –  the timeout value to be used in milliseconds.
Throws:
IOException – if an error occurs during the connection
SocketTimeoutException – if timeout expires before connecting
IllegalBlockingModeException – 
         if this socket has an associated channel,
         and the channel is in non-blocking mode
IllegalArgumentException – if endpoint is null or is a
         SocketAddress subclass not supported by this socket
Since:
1.4
@spec
JSR-51/**
     * Connects this socket to the server with a specified timeout value.
     * A timeout of zero is interpreted as an infinite timeout. The connection
     * will then block until established or an error occurs.
     *
     * @param   endpoint the {@code SocketAddress}
     * @param   timeout  the timeout value to be used in milliseconds.
     * @throws  IOException if an error occurs during the connection
     * @throws  SocketTimeoutException if timeout expires before connecting
     * @throws  java.nio.channels.IllegalBlockingModeException
     *          if this socket has an associated channel,
     *          and the channel is in non-blocking mode
     * @throws  IllegalArgumentException if endpoint is null or is a
     *          SocketAddress subclass not supported by this socket
     * @since 1.4
     * @spec JSR-51
     */
    public void connect(SocketAddress endpoint, int timeout) throws IOException {
        if (endpoint == null)
            throw new IllegalArgumentException("connect: The address can't be null");

        if (timeout < 0)
          throw new IllegalArgumentException("connect: timeout can't be negative");

        if (isClosed())
            throw new SocketException("Socket is closed");

        if (!oldImpl && isConnected())
            throw new SocketException("already connected");

        if (!(endpoint instanceof InetSocketAddress))
            throw new IllegalArgumentException("Unsupported address type");

        InetSocketAddress epoint = (InetSocketAddress) endpoint;
        InetAddress addr = epoint.getAddress ();
        int port = epoint.getPort();
        checkAddress(addr, "connect");

        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            if (epoint.isUnresolved())
                security.checkConnect(epoint.getHostName(), port);
            else
                security.checkConnect(addr.getHostAddress(), port);
        }
        if (!created)
            createImpl(true);
        if (!oldImpl)
            impl.connect(epoint, timeout);
        else if (timeout == 0) {
            if (epoint.isUnresolved())
                impl.connect(addr.getHostName(), port);
            else
                impl.connect(addr, port);
        } else
            throw new UnsupportedOperationException("SocketImpl.connect(addr, timeout)");
        connected = true;
        /*
         * If the socket was not bound before the connect, it is now because
         * the kernel will have picked an ephemeral port & a local address
         */
        bound = true;
    }

    
Binds the socket to a local address.
 If the address is null, then the system will pick up an ephemeral port and a valid local address to bind the socket. 
Params:
bindpoint – the SocketAddress to bind to
Throws:
IOException – if the bind operation fails, or if the socket
                    is already bound.
IllegalArgumentException – if bindpoint is a
         SocketAddress subclass not supported by this socket
SecurityException –  if a security manager exists and its checkListen method doesn't allow the bind to the local port.
See Also:
isBound
Since:
  1.4/**
     * Binds the socket to a local address.
     * <P>
     * If the address is {@code null}, then the system will pick up
     * an ephemeral port and a valid local address to bind the socket.
     *
     * @param   bindpoint the {@code SocketAddress} to bind to
     * @throws  IOException if the bind operation fails, or if the socket
     *                     is already bound.
     * @throws  IllegalArgumentException if bindpoint is a
     *          SocketAddress subclass not supported by this socket
     * @throws  SecurityException  if a security manager exists and its
     *          {@code checkListen} method doesn't allow the bind
     *          to the local port.
     *
     * @since   1.4
     * @see #isBound
     */
    public void bind(SocketAddress bindpoint) throws IOException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        if (!oldImpl && isBound())
            throw new SocketException("Already bound");

        if (bindpoint != null && (!(bindpoint instanceof InetSocketAddress)))
            throw new IllegalArgumentException("Unsupported address type");
        InetSocketAddress epoint = (InetSocketAddress) bindpoint;
        if (epoint != null && epoint.isUnresolved())
            throw new SocketException("Unresolved address");
        if (epoint == null) {
            epoint = new InetSocketAddress(0);
        }
        InetAddress addr = epoint.getAddress();
        int port = epoint.getPort();
        checkAddress (addr, "bind");
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkListen(port);
        }
        getImpl().bind (addr, port);
        bound = true;
    }

    private void checkAddress (InetAddress addr, String op) {
        if (addr == null) {
            return;
        }
        if (!(addr instanceof Inet4Address || addr instanceof Inet6Address)) {
            throw new IllegalArgumentException(op + ": invalid address type");
        }
    }

    
set the flags after an accept() call.
/**
     * set the flags after an accept() call.
     */
    final void postAccept() {
        connected = true;
        created = true;
        bound = true;
    }

    void setCreated() {
        created = true;
    }

    void setBound() {
        bound = true;
    }

    void setConnected() {
        connected = true;
    }

    
Returns the address to which the socket is connected.
 If the socket was connected prior to being closed, then this method will continue to return the connected address after the socket is closed. 
Returns:
 the remote IP address to which this socket is connected, or null if the socket is not connected./**
     * Returns the address to which the socket is connected.
     * <p>
     * If the socket was connected prior to being {@link #close closed},
     * then this method will continue to return the connected address
     * after the socket is closed.
     *
     * @return  the remote IP address to which this socket is connected,
     *          or {@code null} if the socket is not connected.
     */
    public InetAddress getInetAddress() {
        if (!isConnected())
            return null;
        try {
            return getImpl().getInetAddress();
        } catch (SocketException e) {
        }
        return null;
    }

    
Gets the local address to which the socket is bound.
 If there is a security manager set, its checkConnect method is called with the local address and -1 as its arguments to see if the operation is allowed. If the operation is not allowed, the loopback address is returned. 
See Also:
SecurityManager.checkConnect
Returns:
the local address to which the socket is bound,
        the loopback address if denied by the security manager, or
        the wildcard address if the socket is closed or not bound yet.
Since:
  1.1/**
     * Gets the local address to which the socket is bound.
     * <p>
     * If there is a security manager set, its {@code checkConnect} method is
     * called with the local address and {@code -1} as its arguments to see
     * if the operation is allowed. If the operation is not allowed,
     * the {@link InetAddress#getLoopbackAddress loopback} address is returned.
     *
     * @return the local address to which the socket is bound,
     *         the loopback address if denied by the security manager, or
     *         the wildcard address if the socket is closed or not bound yet.
     * @since   1.1
     *
     * @see SecurityManager#checkConnect
     */
    public InetAddress getLocalAddress() {
        // This is for backward compatibility
        if (!isBound())
            return InetAddress.anyLocalAddress();
        InetAddress in = null;
        try {
            in = (InetAddress) getImpl().getOption(SocketOptions.SO_BINDADDR);
            SecurityManager sm = System.getSecurityManager();
            if (sm != null)
                sm.checkConnect(in.getHostAddress(), -1);
            if (in.isAnyLocalAddress()) {
                in = InetAddress.anyLocalAddress();
            }
        } catch (SecurityException e) {
            in = InetAddress.getLoopbackAddress();
        } catch (Exception e) {
            in = InetAddress.anyLocalAddress(); // "0.0.0.0"
        }
        return in;
    }

    
Returns the remote port number to which this socket is connected.
 If the socket was connected prior to being closed, then this method will continue to return the connected port number after the socket is closed. 
Returns:
 the remote port number to which this socket is connected, or
         0 if the socket is not connected yet./**
     * Returns the remote port number to which this socket is connected.
     * <p>
     * If the socket was connected prior to being {@link #close closed},
     * then this method will continue to return the connected port number
     * after the socket is closed.
     *
     * @return  the remote port number to which this socket is connected, or
     *          0 if the socket is not connected yet.
     */
    public int getPort() {
        if (!isConnected())
            return 0;
        try {
            return getImpl().getPort();
        } catch (SocketException e) {
            // Shouldn't happen as we're connected
        }
        return -1;
    }

    
Returns the local port number to which this socket is bound.
 If the socket was bound prior to being closed, then this method will continue to return the local port number after the socket is closed. 
Returns:
 the local port number to which this socket is bound or -1
         if the socket is not bound yet./**
     * Returns the local port number to which this socket is bound.
     * <p>
     * If the socket was bound prior to being {@link #close closed},
     * then this method will continue to return the local port number
     * after the socket is closed.
     *
     * @return  the local port number to which this socket is bound or -1
     *          if the socket is not bound yet.
     */
    public int getLocalPort() {
        if (!isBound())
            return -1;
        try {
            return getImpl().getLocalPort();
        } catch(SocketException e) {
            // shouldn't happen as we're bound
        }
        return -1;
    }

    
Returns the address of the endpoint this socket is connected to, or null if it is unconnected. 
 If the socket was connected prior to being closed, then this method will continue to return the connected address after the socket is closed. 
See Also:
getInetAddress()
getPort()
connect(SocketAddress, int)
connect(SocketAddress)
Returns:
a SocketAddress representing the remote endpoint of this socket, or null if it is not connected yet.
Since:
1.4/**
     * Returns the address of the endpoint this socket is connected to, or
     * {@code null} if it is unconnected.
     * <p>
     * If the socket was connected prior to being {@link #close closed},
     * then this method will continue to return the connected address
     * after the socket is closed.
     *

     * @return a {@code SocketAddress} representing the remote endpoint of this
     *         socket, or {@code null} if it is not connected yet.
     * @see #getInetAddress()
     * @see #getPort()
     * @see #connect(SocketAddress, int)
     * @see #connect(SocketAddress)
     * @since 1.4
     */
    public SocketAddress getRemoteSocketAddress() {
        if (!isConnected())
            return null;
        return new InetSocketAddress(getInetAddress(), getPort());
    }

    
Returns the address of the endpoint this socket is bound to.
 If a socket bound to an endpoint represented by an InetSocketAddress  is closed, then this method will continue to return an InetSocketAddress after the socket is closed. In that case the returned InetSocketAddress's address is the wildcard address and its port is the local port that it was bound to. 
 If there is a security manager set, its checkConnect method is called with the local address and -1 as its arguments to see if the operation is allowed. If the operation is not allowed, a SocketAddress representing the loopback address and the local port to which this socket is bound is returned. 
See Also:
getLocalAddress()
getLocalPort()
bind(SocketAddress)
SecurityManager.checkConnect
Returns:
a SocketAddress representing the local endpoint of this socket, or a SocketAddress representing the loopback address if denied by the security manager, or null if the socket is not bound yet.
Since:
1.4/**
     * Returns the address of the endpoint this socket is bound to.
     * <p>
     * If a socket bound to an endpoint represented by an
     * {@code InetSocketAddress } is {@link #close closed},
     * then this method will continue to return an {@code InetSocketAddress}
     * after the socket is closed. In that case the returned
     * {@code InetSocketAddress}'s address is the
     * {@link InetAddress#isAnyLocalAddress wildcard} address
     * and its port is the local port that it was bound to.
     * <p>
     * If there is a security manager set, its {@code checkConnect} method is
     * called with the local address and {@code -1} as its arguments to see
     * if the operation is allowed. If the operation is not allowed,
     * a {@code SocketAddress} representing the
     * {@link InetAddress#getLoopbackAddress loopback} address and the local
     * port to which this socket is bound is returned.
     *
     * @return a {@code SocketAddress} representing the local endpoint of
     *         this socket, or a {@code SocketAddress} representing the
     *         loopback address if denied by the security manager, or
     *         {@code null} if the socket is not bound yet.
     *
     * @see #getLocalAddress()
     * @see #getLocalPort()
     * @see #bind(SocketAddress)
     * @see SecurityManager#checkConnect
     * @since 1.4
     */

    public SocketAddress getLocalSocketAddress() {
        if (!isBound())
            return null;
        return new InetSocketAddress(getLocalAddress(), getLocalPort());
    }

    
Returns the unique SocketChannel object associated with this socket, if any. 
 A socket will have a channel if, and only if, the channel itself was created via the 
SocketChannel.open or ServerSocketChannel.accept methods. 
Returns:
 the socket channel associated with this socket, or null if this socket was not created for a channel
Since:
1.4
@spec
JSR-51/**
     * Returns the unique {@link java.nio.channels.SocketChannel SocketChannel}
     * object associated with this socket, if any.
     *
     * <p> A socket will have a channel if, and only if, the channel itself was
     * created via the {@link java.nio.channels.SocketChannel#open
     * SocketChannel.open} or {@link
     * java.nio.channels.ServerSocketChannel#accept ServerSocketChannel.accept}
     * methods.
     *
     * @return  the socket channel associated with this socket,
     *          or {@code null} if this socket was not created
     *          for a channel
     *
     * @since 1.4
     * @spec JSR-51
     */
    public SocketChannel getChannel() {
        return null;
    }

    
Returns an input stream for this socket.
 If this socket has an associated channel then the resulting input stream delegates all of its operations to the channel. If the channel is in non-blocking mode then the input stream's read operations will throw an IllegalBlockingModeException. 
Under abnormal conditions the underlying connection may be
broken by the remote host or the network software (for example
a connection reset in the case of TCP connections). When a
broken connection is detected by the network software the
following applies to the returned input stream :-

  
The network software may discard bytes that are buffered by the socket. Bytes that aren't discarded by the network software can be read using read. 
If there are no bytes buffered on the socket, or all buffered bytes have been consumed by read, then all subsequent calls to read will throw an IOException. 
If there are no bytes buffered on the socket, and the socket has not been closed using close, then available will return 0. 
 Closing the returned InputStream will close the associated socket. 
Throws:
IOException –  if an I/O error occurs when creating the input stream, the socket is closed, the socket is not connected, or the socket input has been shutdown using shutdownInput()
Returns:
    an input stream for reading bytes from this socket.
@revised
1.4
@spec
JSR-51/**
     * Returns an input stream for this socket.
     *
     * <p> If this socket has an associated channel then the resulting input
     * stream delegates all of its operations to the channel.  If the channel
     * is in non-blocking mode then the input stream's {@code read} operations
     * will throw an {@link java.nio.channels.IllegalBlockingModeException}.
     *
     * <p>Under abnormal conditions the underlying connection may be
     * broken by the remote host or the network software (for example
     * a connection reset in the case of TCP connections). When a
     * broken connection is detected by the network software the
     * following applies to the returned input stream :-
     *
     * <ul>
     *
     *   <li><p>The network software may discard bytes that are buffered
     *   by the socket. Bytes that aren't discarded by the network
     *   software can be read using {@link java.io.InputStream#read read}.
     *
     *   <li><p>If there are no bytes buffered on the socket, or all
     *   buffered bytes have been consumed by
     *   {@link java.io.InputStream#read read}, then all subsequent
     *   calls to {@link java.io.InputStream#read read} will throw an
     *   {@link java.io.IOException IOException}.
     *
     *   <li><p>If there are no bytes buffered on the socket, and the
     *   socket has not been closed using {@link #close close}, then
     *   {@link java.io.InputStream#available available} will
     *   return {@code 0}.
     *
     * </ul>
     *
     * <p> Closing the returned {@link java.io.InputStream InputStream}
     * will close the associated socket.
     *
     * @return     an input stream for reading bytes from this socket.
     * @exception  IOException  if an I/O error occurs when creating the
     *             input stream, the socket is closed, the socket is
     *             not connected, or the socket input has been shutdown
     *             using {@link #shutdownInput()}
     *
     * @revised 1.4
     * @spec JSR-51
     */
    public InputStream getInputStream() throws IOException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        if (!isConnected())
            throw new SocketException("Socket is not connected");
        if (isInputShutdown())
            throw new SocketException("Socket input is shutdown");
        InputStream is = null;
        try {
            is = AccessController.doPrivileged(
                new PrivilegedExceptionAction<>() {
                    public InputStream run() throws IOException {
                        return impl.getInputStream();
                    }
                });
        } catch (java.security.PrivilegedActionException e) {
            throw (IOException) e.getException();
        }
        return is;
    }

    
Returns an output stream for this socket.
 If this socket has an associated channel then the resulting output stream delegates all of its operations to the channel. If the channel is in non-blocking mode then the output stream's write operations will throw an IllegalBlockingModeException. 
 Closing the returned OutputStream will close the associated socket. 
Throws:
IOException –  if an I/O error occurs when creating the
              output stream or if the socket is not connected.
Returns:
    an output stream for writing bytes to this socket.
@revised
1.4
@spec
JSR-51/**
     * Returns an output stream for this socket.
     *
     * <p> If this socket has an associated channel then the resulting output
     * stream delegates all of its operations to the channel.  If the channel
     * is in non-blocking mode then the output stream's {@code write}
     * operations will throw an {@link
     * java.nio.channels.IllegalBlockingModeException}.
     *
     * <p> Closing the returned {@link java.io.OutputStream OutputStream}
     * will close the associated socket.
     *
     * @return     an output stream for writing bytes to this socket.
     * @exception  IOException  if an I/O error occurs when creating the
     *               output stream or if the socket is not connected.
     * @revised 1.4
     * @spec JSR-51
     */
    public OutputStream getOutputStream() throws IOException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        if (!isConnected())
            throw new SocketException("Socket is not connected");
        if (isOutputShutdown())
            throw new SocketException("Socket output is shutdown");
        OutputStream os = null;
        try {
            os = AccessController.doPrivileged(
                new PrivilegedExceptionAction<>() {
                    public OutputStream run() throws IOException {
                        return impl.getOutputStream();
                    }
                });
        } catch (java.security.PrivilegedActionException e) {
            throw (IOException) e.getException();
        }
        return os;
    }

    
Enable/disable TCP_NODELAY (disable/enable Nagle's algorithm). 
Params:
on – true to enable TCP_NODELAY, false to disable.
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
getTcpNoDelay()
Since:
  1.1/**
     * Enable/disable {@link SocketOptions#TCP_NODELAY TCP_NODELAY}
     * (disable/enable Nagle's algorithm).
     *
     * @param on {@code true} to enable TCP_NODELAY,
     * {@code false} to disable.
     *
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     *
     * @since   1.1
     *
     * @see #getTcpNoDelay()
     */
    public void setTcpNoDelay(boolean on) throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.TCP_NODELAY, Boolean.valueOf(on));
    }

    
Tests if TCP_NODELAY is enabled. 
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
setTcpNoDelay(boolean)
Returns:
a boolean indicating whether or not TCP_NODELAY is enabled.
Since:
  1.1/**
     * Tests if {@link SocketOptions#TCP_NODELAY TCP_NODELAY} is enabled.
     *
     * @return a {@code boolean} indicating whether or not
     *         {@link SocketOptions#TCP_NODELAY TCP_NODELAY} is enabled.
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     * @since   1.1
     * @see #setTcpNoDelay(boolean)
     */
    public boolean getTcpNoDelay() throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        return ((Boolean) getImpl().getOption(SocketOptions.TCP_NODELAY)).booleanValue();
    }

    
Enable/disable SO_LINGER with the specified linger time in seconds. The maximum timeout value is platform specific. The setting only affects socket close. 
Params:
on –     whether or not to linger on.
linger – how long to linger for, if on is true.
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
IllegalArgumentException – if the linger value is negative.
See Also:
getSoLinger()
Since:
1.1/**
     * Enable/disable {@link SocketOptions#SO_LINGER SO_LINGER} with the
     * specified linger time in seconds. The maximum timeout value is platform
     * specific.
     *
     * The setting only affects socket close.
     *
     * @param on     whether or not to linger on.
     * @param linger how long to linger for, if on is true.
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     * @exception IllegalArgumentException if the linger value is negative.
     * @since 1.1
     * @see #getSoLinger()
     */
    public void setSoLinger(boolean on, int linger) throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        if (!on) {
            getImpl().setOption(SocketOptions.SO_LINGER, on);
        } else {
            if (linger < 0) {
                throw new IllegalArgumentException("invalid value for SO_LINGER");
            }
            if (linger > 65535)
                linger = 65535;
            getImpl().setOption(SocketOptions.SO_LINGER, linger);
        }
    }

    
Returns setting for SO_LINGER. -1 returns implies that the option is disabled. The setting only affects socket close. 
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
setSoLinger(boolean, int)
Returns:
the setting for SO_LINGER.
Since:
  1.1/**
     * Returns setting for {@link SocketOptions#SO_LINGER SO_LINGER}.
     * -1 returns implies that the
     * option is disabled.
     *
     * The setting only affects socket close.
     *
     * @return the setting for {@link SocketOptions#SO_LINGER SO_LINGER}.
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     * @since   1.1
     * @see #setSoLinger(boolean, int)
     */
    public int getSoLinger() throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        Object o = getImpl().getOption(SocketOptions.SO_LINGER);
        if (o instanceof Integer) {
            return ((Integer) o).intValue();
        } else {
            return -1;
        }
    }

    
Send one byte of urgent data on the socket. The byte to be sent is the lowest eight
bits of the data parameter. The urgent byte is
sent after any preceding writes to the socket OutputStream
and before any future writes to the OutputStream.
Params:
data – The byte of data to send
Throws:
IOException – if there is an error
 sending the data.
Since:
1.4/**
     * Send one byte of urgent data on the socket. The byte to be sent is the lowest eight
     * bits of the data parameter. The urgent byte is
     * sent after any preceding writes to the socket OutputStream
     * and before any future writes to the OutputStream.
     * @param data The byte of data to send
     * @exception IOException if there is an error
     *  sending the data.
     * @since 1.4
     */
    public void sendUrgentData (int data) throws IOException  {
        if (!getImpl().supportsUrgentData ()) {
            throw new SocketException ("Urgent data not supported");
        }
        getImpl().sendUrgentData (data);
    }

    
Enable/disable SO_OOBINLINE (receipt of TCP urgent data) By default, this option is disabled and TCP urgent data received on a socket is silently discarded. If the user wishes to receive urgent data, then this option must be enabled. When enabled, urgent data is received inline with normal data. 

Note, only limited support is provided for handling incoming urgent
data. In particular, no notification of incoming urgent data is provided
and there is no capability to distinguish between normal data and urgent
data unless provided by a higher level protocol.
Params:
on – true to enable SO_OOBINLINE, false to disable.
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
getOOBInline()
Since:
  1.4/**
     * Enable/disable {@link SocketOptions#SO_OOBINLINE SO_OOBINLINE}
     * (receipt of TCP urgent data)
     *
     * By default, this option is disabled and TCP urgent data received on a
     * socket is silently discarded. If the user wishes to receive urgent data, then
     * this option must be enabled. When enabled, urgent data is received
     * inline with normal data.
     * <p>
     * Note, only limited support is provided for handling incoming urgent
     * data. In particular, no notification of incoming urgent data is provided
     * and there is no capability to distinguish between normal data and urgent
     * data unless provided by a higher level protocol.
     *
     * @param on {@code true} to enable
     *           {@link SocketOptions#SO_OOBINLINE SO_OOBINLINE},
     *           {@code false} to disable.
     *
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     *
     * @since   1.4
     *
     * @see #getOOBInline()
     */
    public void setOOBInline(boolean on) throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.SO_OOBINLINE, Boolean.valueOf(on));
    }

    
Tests if SO_OOBINLINE is enabled. 
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
setOOBInline(boolean)
Returns:
a boolean indicating whether or not SO_OOBINLINEis enabled.
Since:
  1.4/**
     * Tests if {@link SocketOptions#SO_OOBINLINE SO_OOBINLINE} is enabled.
     *
     * @return a {@code boolean} indicating whether or not
     *         {@link SocketOptions#SO_OOBINLINE SO_OOBINLINE}is enabled.
     *
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     * @since   1.4
     * @see #setOOBInline(boolean)
     */
    public boolean getOOBInline() throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        return ((Boolean) getImpl().getOption(SocketOptions.SO_OOBINLINE)).booleanValue();
    }

    
 Enable/disable SO_TIMEOUT with the specified timeout, in milliseconds. With this option set to a non-zero timeout, a read() call on the InputStream associated with this Socket will block for only this amount of time. If the timeout expires, a java.net.SocketTimeoutException is raised, though the
 Socket is still valid. The option must be enabled prior to entering the blocking operation to have effect. The timeout must be > 0. A timeout of zero is interpreted as an infinite timeout. 
Params:
timeout – the specified timeout, in milliseconds.
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
getSoTimeout()
Since:
  1.1/**
     *  Enable/disable {@link SocketOptions#SO_TIMEOUT SO_TIMEOUT}
     *  with the specified timeout, in milliseconds. With this option set
     *  to a non-zero timeout, a read() call on the InputStream associated with
     *  this Socket will block for only this amount of time.  If the timeout
     *  expires, a <B>java.net.SocketTimeoutException</B> is raised, though the
     *  Socket is still valid. The option <B>must</B> be enabled
     *  prior to entering the blocking operation to have effect. The
     *  timeout must be {@code > 0}.
     *  A timeout of zero is interpreted as an infinite timeout.
     *
     * @param timeout the specified timeout, in milliseconds.
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     * @since   1.1
     * @see #getSoTimeout()
     */
    public synchronized void setSoTimeout(int timeout) throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        if (timeout < 0)
          throw new IllegalArgumentException("timeout can't be negative");

        getImpl().setOption(SocketOptions.SO_TIMEOUT, timeout);
    }

    
Returns setting for SO_TIMEOUT. 0 returns implies that the option is disabled (i.e., timeout of infinity). 
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
setSoTimeout(int)
Returns:
the setting for SO_TIMEOUT
Since:
  1.1/**
     * Returns setting for {@link SocketOptions#SO_TIMEOUT SO_TIMEOUT}.
     * 0 returns implies that the option is disabled (i.e., timeout of infinity).
     *
     * @return the setting for {@link SocketOptions#SO_TIMEOUT SO_TIMEOUT}
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     *
     * @since   1.1
     * @see #setSoTimeout(int)
     */
    public synchronized int getSoTimeout() throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        Object o = getImpl().getOption(SocketOptions.SO_TIMEOUT);
        /* extra type safety */
        if (o instanceof Integer) {
            return ((Integer) o).intValue();
        } else {
            return 0;
        }
    }

    
Sets the SO_SNDBUF option to the specified value for this Socket. The SO_SNDBUF option is used by the platform's networking code as a hint for the size to set the underlying network I/O buffers. 
Because SO_SNDBUF is a hint, applications that want to verify what size the buffers were set to should call getSendBufferSize(). 
Params:
size – the size to which to set the send buffer
size. This value must be greater than 0.
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
IllegalArgumentException – if the
value is 0 or is negative.
See Also:
getSendBufferSize()
Since:
1.2/**
     * Sets the {@link SocketOptions#SO_SNDBUF SO_SNDBUF} option to the
     * specified value for this {@code Socket}.
     * The {@link SocketOptions#SO_SNDBUF SO_SNDBUF} option is used by the
     * platform's networking code as a hint for the size to set the underlying
     * network I/O buffers.
     *
     * <p>Because {@link SocketOptions#SO_SNDBUF SO_SNDBUF} is a hint,
     * applications that want to verify what size the buffers were set to
     * should call {@link #getSendBufferSize()}.
     *
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     *
     * @param size the size to which to set the send buffer
     * size. This value must be greater than 0.
     *
     * @exception IllegalArgumentException if the
     * value is 0 or is negative.
     *
     * @see #getSendBufferSize()
     * @since 1.2
     */
    public synchronized void setSendBufferSize(int size)
    throws SocketException{
        if (!(size > 0)) {
            throw new IllegalArgumentException("negative send size");
        }
        if (isClosed())
            throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.SO_SNDBUF, size);
    }

    
Get value of the SO_SNDBUF option for this Socket, that is the buffer size used by the platform for output on this Socket. 
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
setSendBufferSize(int)
Returns:
the value of the SO_SNDBUF option for this Socket.
Since:
1.2/**
     * Get value of the {@link SocketOptions#SO_SNDBUF SO_SNDBUF} option
     * for this {@code Socket}, that is the buffer size used by the platform
     * for output on this {@code Socket}.
     * @return the value of the {@link SocketOptions#SO_SNDBUF SO_SNDBUF}
     *         option for this {@code Socket}.
     *
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     *
     * @see #setSendBufferSize(int)
     * @since 1.2
     */
    public synchronized int getSendBufferSize() throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        int result = 0;
        Object o = getImpl().getOption(SocketOptions.SO_SNDBUF);
        if (o instanceof Integer) {
            result = ((Integer)o).intValue();
        }
        return result;
    }

    
Sets the SO_RCVBUF option to the specified value for this Socket. The SO_RCVBUF option is used by the platform's networking code as a hint for the size to set the underlying network I/O buffers. 
Increasing the receive buffer size can increase the performance of
network I/O for high-volume connection, while decreasing it can
help reduce the backlog of incoming data.
Because SO_RCVBUF is a hint, applications that want to verify what size the buffers were set to should call getReceiveBufferSize(). 
The value of SO_RCVBUF is also used to set the TCP receive window that is advertized to the remote peer. Generally, the window size can be modified at any time when a socket is connected. However, if a receive window larger than 64K is required then this must be requested before the socket is connected to the
remote peer. There are two cases to be aware of:

For sockets accepted from a ServerSocket, this must be done by calling ServerSocket.setReceiveBufferSize(int) before the ServerSocket is bound to a local address.
For client sockets, setReceiveBufferSize() must be called before
connecting the socket to its remote peer.
Params:
size – the size to which to set the receive buffer
size. This value must be greater than 0.
Throws:
IllegalArgumentException – if the value is 0 or is
negative.
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
getReceiveBufferSize()
ServerSocket.setReceiveBufferSize(int)
Since:
1.2/**
     * Sets the {@link SocketOptions#SO_RCVBUF SO_RCVBUF} option to the
     * specified value for this {@code Socket}. The
     * {@link SocketOptions#SO_RCVBUF SO_RCVBUF} option is
     * used by the platform's networking code as a hint for the size to set
     * the underlying network I/O buffers.
     *
     * <p>Increasing the receive buffer size can increase the performance of
     * network I/O for high-volume connection, while decreasing it can
     * help reduce the backlog of incoming data.
     *
     * <p>Because {@link SocketOptions#SO_RCVBUF SO_RCVBUF} is a hint,
     * applications that want to verify what size the buffers were set to
     * should call {@link #getReceiveBufferSize()}.
     *
     * <p>The value of {@link SocketOptions#SO_RCVBUF SO_RCVBUF} is also used
     * to set the TCP receive window that is advertized to the remote peer.
     * Generally, the window size can be modified at any time when a socket is
     * connected. However, if a receive window larger than 64K is required then
     * this must be requested <B>before</B> the socket is connected to the
     * remote peer. There are two cases to be aware of:
     * <ol>
     * <li>For sockets accepted from a ServerSocket, this must be done by calling
     * {@link ServerSocket#setReceiveBufferSize(int)} before the ServerSocket
     * is bound to a local address.</li>
     * <li>For client sockets, setReceiveBufferSize() must be called before
     * connecting the socket to its remote peer.</li></ol>
     * @param size the size to which to set the receive buffer
     * size. This value must be greater than 0.
     *
     * @exception IllegalArgumentException if the value is 0 or is
     * negative.
     *
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     *
     * @see #getReceiveBufferSize()
     * @see ServerSocket#setReceiveBufferSize(int)
     * @since 1.2
     */
    public synchronized void setReceiveBufferSize(int size)
    throws SocketException{
        if (size <= 0) {
            throw new IllegalArgumentException("invalid receive size");
        }
        if (isClosed())
            throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.SO_RCVBUF, size);
    }

    
Gets the value of the SO_RCVBUF option for this Socket, that is the buffer size used by the platform for input on this Socket. 
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
setReceiveBufferSize(int)
Returns:
the value of the SO_RCVBUF option for this Socket.
Since:
1.2/**
     * Gets the value of the {@link SocketOptions#SO_RCVBUF SO_RCVBUF} option
     * for this {@code Socket}, that is the buffer size used by the platform
     * for input on this {@code Socket}.
     *
     * @return the value of the {@link SocketOptions#SO_RCVBUF SO_RCVBUF}
     *         option for this {@code Socket}.
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     * @see #setReceiveBufferSize(int)
     * @since 1.2
     */
    public synchronized int getReceiveBufferSize()
    throws SocketException{
        if (isClosed())
            throw new SocketException("Socket is closed");
        int result = 0;
        Object o = getImpl().getOption(SocketOptions.SO_RCVBUF);
        if (o instanceof Integer) {
            result = ((Integer)o).intValue();
        }
        return result;
    }

    
Enable/disable SO_KEEPALIVE. 
Params:
on –  whether or not to have socket keep alive turned on.
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
getKeepAlive()
Since:
1.3/**
     * Enable/disable {@link SocketOptions#SO_KEEPALIVE SO_KEEPALIVE}.
     *
     * @param on  whether or not to have socket keep alive turned on.
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     * @since 1.3
     * @see #getKeepAlive()
     */
    public void setKeepAlive(boolean on) throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.SO_KEEPALIVE, Boolean.valueOf(on));
    }

    
Tests if SO_KEEPALIVE is enabled. 
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
setKeepAlive(boolean)
Returns:
a boolean indicating whether or not SO_KEEPALIVE is enabled.
Since:
  1.3/**
     * Tests if {@link SocketOptions#SO_KEEPALIVE SO_KEEPALIVE} is enabled.
     *
     * @return a {@code boolean} indicating whether or not
     *         {@link SocketOptions#SO_KEEPALIVE SO_KEEPALIVE} is enabled.
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     * @since   1.3
     * @see #setKeepAlive(boolean)
     */
    public boolean getKeepAlive() throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        return ((Boolean) getImpl().getOption(SocketOptions.SO_KEEPALIVE)).booleanValue();
    }

    
Sets traffic class or type-of-service octet in the IP
header for packets sent from this Socket.
As the underlying network implementation may ignore this
value applications should consider it a hint.
 The tc must be in the range 0 <= tc <=
255 or an IllegalArgumentException will be thrown. 
Notes:
For Internet Protocol v4 the value consists of an integer, the least significant 8 bits of which represent the value of the TOS octet in IP packets sent by the socket. RFC 1349 defines the TOS values as follows: 

IPTOS_LOWCOST (0x02)
IPTOS_RELIABILITY (0x04)
IPTOS_THROUGHPUT (0x08)
IPTOS_LOWDELAY (0x10)

The last low order bit is always ignored as this
corresponds to the MBZ (must be zero) bit.

Setting bits in the precedence field may result in a
SocketException indicating that the operation is not
permitted.

As RFC 1122 section 4.2.4.2 indicates, a compliant TCP
implementation should, but is not required to, let application
change the TOS field during the lifetime of a connection.
So whether the type-of-service field can be changed after the
TCP connection has been established depends on the implementation
in the underlying platform. Applications should not assume that
they can change the TOS field after the connection.
 For Internet Protocol v6 tc is the value that would be placed into the sin6_flowinfo field of the IP header. 
Params:
tc –  an int value for the bitset.
Throws:
SocketException – if there is an error setting the
traffic class or type-of-service
See Also:
getTrafficClass
SocketOptions.IP_TOS
Since:
1.4/**
     * Sets traffic class or type-of-service octet in the IP
     * header for packets sent from this Socket.
     * As the underlying network implementation may ignore this
     * value applications should consider it a hint.
     *
     * <P> The tc <B>must</B> be in the range {@code 0 <= tc <=
     * 255} or an IllegalArgumentException will be thrown.
     * <p>Notes:
     * <p>For Internet Protocol v4 the value consists of an
     * {@code integer}, the least significant 8 bits of which
     * represent the value of the TOS octet in IP packets sent by
     * the socket.
     * RFC 1349 defines the TOS values as follows:
     *
     * <UL>
     * <LI><CODE>IPTOS_LOWCOST (0x02)</CODE></LI>
     * <LI><CODE>IPTOS_RELIABILITY (0x04)</CODE></LI>
     * <LI><CODE>IPTOS_THROUGHPUT (0x08)</CODE></LI>
     * <LI><CODE>IPTOS_LOWDELAY (0x10)</CODE></LI>
     * </UL>
     * The last low order bit is always ignored as this
     * corresponds to the MBZ (must be zero) bit.
     * <p>
     * Setting bits in the precedence field may result in a
     * SocketException indicating that the operation is not
     * permitted.
     * <p>
     * As RFC 1122 section 4.2.4.2 indicates, a compliant TCP
     * implementation should, but is not required to, let application
     * change the TOS field during the lifetime of a connection.
     * So whether the type-of-service field can be changed after the
     * TCP connection has been established depends on the implementation
     * in the underlying platform. Applications should not assume that
     * they can change the TOS field after the connection.
     * <p>
     * For Internet Protocol v6 {@code tc} is the value that
     * would be placed into the sin6_flowinfo field of the IP header.
     *
     * @param tc        an {@code int} value for the bitset.
     * @throws SocketException if there is an error setting the
     * traffic class or type-of-service
     * @since 1.4
     * @see #getTrafficClass
     * @see SocketOptions#IP_TOS
     */
    public void setTrafficClass(int tc) throws SocketException {
        if (tc < 0 || tc > 255)
            throw new IllegalArgumentException("tc is not in range 0 -- 255");

        if (isClosed())
            throw new SocketException("Socket is closed");
        try {
            getImpl().setOption(SocketOptions.IP_TOS, tc);
        } catch (SocketException se) {
            // not supported if socket already connected
            // Solaris returns error in such cases
            if(!isConnected())
                throw se;
        }
    }

    
Gets traffic class or type-of-service in the IP header
for packets sent from this Socket
 As the underlying network implementation may ignore the traffic class or type-of-service set using setTrafficClass(int) this method may return a different value than was previously set using the setTrafficClass(int) method on this Socket. 
Throws:
SocketException – if there is an error obtaining the
traffic class or type-of-service value.
See Also:
setTrafficClass(int)
SocketOptions.IP_TOS
Returns:
the traffic class or type-of-service already set
Since:
1.4/**
     * Gets traffic class or type-of-service in the IP header
     * for packets sent from this Socket
     * <p>
     * As the underlying network implementation may ignore the
     * traffic class or type-of-service set using {@link #setTrafficClass(int)}
     * this method may return a different value than was previously
     * set using the {@link #setTrafficClass(int)} method on this Socket.
     *
     * @return the traffic class or type-of-service already set
     * @throws SocketException if there is an error obtaining the
     * traffic class or type-of-service value.
     * @since 1.4
     * @see #setTrafficClass(int)
     * @see SocketOptions#IP_TOS
     */
    public int getTrafficClass() throws SocketException {
        return ((Integer) (getImpl().getOption(SocketOptions.IP_TOS))).intValue();
    }

    
Enable/disable the SO_REUSEADDR socket option. 
 When a TCP connection is closed the connection may remain in a timeout state for a period of time after the connection is closed (typically known as the TIME_WAIT state or 2MSL wait state). For applications using a well known socket address or port it may not be possible to bind a socket to the required SocketAddress if there is a connection in the timeout state involving the socket address or port. 
 Enabling SO_REUSEADDR prior to binding the socket using bind(SocketAddress) allows the socket to be bound even though a previous connection is in a timeout state. 
 When a Socket is created the initial setting of SO_REUSEADDR is disabled. 
 The behaviour when SO_REUSEADDR is enabled or disabled after a socket is bound (See isBound()) is not defined. 
Params:
on –  whether to enable or disable the socket option
Throws:
SocketException – if an error occurs enabling or disabling the SO_REUSEADDR socket option, or the socket is closed.
See Also:
getReuseAddress()
bind(SocketAddress)
isClosed()
isBound()
Since:
1.4/**
     * Enable/disable the {@link SocketOptions#SO_REUSEADDR SO_REUSEADDR}
     * socket option.
     * <p>
     * When a TCP connection is closed the connection may remain
     * in a timeout state for a period of time after the connection
     * is closed (typically known as the {@code TIME_WAIT} state
     * or {@code 2MSL} wait state).
     * For applications using a well known socket address or port
     * it may not be possible to bind a socket to the required
     * {@code SocketAddress} if there is a connection in the
     * timeout state involving the socket address or port.
     * <p>
     * Enabling {@link SocketOptions#SO_REUSEADDR SO_REUSEADDR}
     * prior to binding the socket using {@link #bind(SocketAddress)} allows
     * the socket to be bound even though a previous connection is in a timeout
     * state.
     * <p>
     * When a {@code Socket} is created the initial setting
     * of {@link SocketOptions#SO_REUSEADDR SO_REUSEADDR} is disabled.
     * <p>
     * The behaviour when {@link SocketOptions#SO_REUSEADDR SO_REUSEADDR} is
     * enabled or disabled after a socket is bound (See {@link #isBound()})
     * is not defined.
     *
     * @param on  whether to enable or disable the socket option
     * @exception SocketException if an error occurs enabling or
     *            disabling the {@link SocketOptions#SO_REUSEADDR SO_REUSEADDR}
     *            socket option, or the socket is closed.
     * @since 1.4
     * @see #getReuseAddress()
     * @see #bind(SocketAddress)
     * @see #isClosed()
     * @see #isBound()
     */
    public void setReuseAddress(boolean on) throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        getImpl().setOption(SocketOptions.SO_REUSEADDR, Boolean.valueOf(on));
    }

    
Tests if SO_REUSEADDR is enabled. 
Throws:
SocketException – if there is an error
in the underlying protocol, such as a TCP error.
See Also:
setReuseAddress(boolean)
Returns:
a boolean indicating whether or not SO_REUSEADDR is enabled.
Since:
  1.4/**
     * Tests if {@link SocketOptions#SO_REUSEADDR SO_REUSEADDR} is enabled.
     *
     * @return a {@code boolean} indicating whether or not
     *         {@link SocketOptions#SO_REUSEADDR SO_REUSEADDR} is enabled.
     * @exception SocketException if there is an error
     * in the underlying protocol, such as a TCP error.
     * @since   1.4
     * @see #setReuseAddress(boolean)
     */
    public boolean getReuseAddress() throws SocketException {
        if (isClosed())
            throw new SocketException("Socket is closed");
        return ((Boolean) (getImpl().getOption(SocketOptions.SO_REUSEADDR))).booleanValue();
    }

    
Closes this socket.
 Any thread currently blocked in an I/O operation upon this socket will throw a SocketException. 

Once a socket has been closed, it is not available for further networking
use (i.e. can't be reconnected or rebound). A new socket needs to be
created.
 Closing this socket will also close the socket's InputStream and OutputStream. 
 If this socket has an associated channel then the channel is closed
as well.
Throws:
IOException –  if an I/O error occurs when closing this socket.
See Also:
isClosed
@revised
1.4
@spec
JSR-51/**
     * Closes this socket.
     * <p>
     * Any thread currently blocked in an I/O operation upon this socket
     * will throw a {@link SocketException}.
     * <p>
     * Once a socket has been closed, it is not available for further networking
     * use (i.e. can't be reconnected or rebound). A new socket needs to be
     * created.
     *
     * <p> Closing this socket will also close the socket's
     * {@link java.io.InputStream InputStream} and
     * {@link java.io.OutputStream OutputStream}.
     *
     * <p> If this socket has an associated channel then the channel is closed
     * as well.
     *
     * @exception  IOException  if an I/O error occurs when closing this socket.
     * @revised 1.4
     * @spec JSR-51
     * @see #isClosed
     */
    public synchronized void close() throws IOException {
        synchronized(closeLock) {
            if (isClosed())
                return;
            if (created)
                impl.close();
            closed = true;
        }
    }

    
Places the input stream for this socket at "end of stream".
Any data sent to the input stream side of the socket is acknowledged
and then silently discarded.
 If you read from a socket input stream after invoking this method on the socket, the stream's available method will return 0, and its read methods will return -1 (end of stream). 
Throws:
IOException – if an I/O error occurs when shutting down this
socket.
See Also:
shutdownOutput()
close()
setSoLinger(boolean, int)
isInputShutdown
Since:
1.3/**
     * Places the input stream for this socket at "end of stream".
     * Any data sent to the input stream side of the socket is acknowledged
     * and then silently discarded.
     * <p>
     * If you read from a socket input stream after invoking this method on the
     * socket, the stream's {@code available} method will return 0, and its
     * {@code read} methods will return {@code -1} (end of stream).
     *
     * @exception IOException if an I/O error occurs when shutting down this
     * socket.
     *
     * @since 1.3
     * @see java.net.Socket#shutdownOutput()
     * @see java.net.Socket#close()
     * @see java.net.Socket#setSoLinger(boolean, int)
     * @see #isInputShutdown
     */
    public void shutdownInput() throws IOException
    {
        if (isClosed())
            throw new SocketException("Socket is closed");
        if (!isConnected())
            throw new SocketException("Socket is not connected");
        if (isInputShutdown())
            throw new SocketException("Socket input is already shutdown");
        getImpl().shutdownInput();
        shutIn = true;
    }

    
Disables the output stream for this socket.
For a TCP socket, any previously written data will be sent
followed by TCP's normal connection termination sequence.
If you write to a socket output stream after invoking
shutdownOutput() on the socket, the stream will throw
an IOException.
Throws:
IOException – if an I/O error occurs when shutting down this
socket.
See Also:
shutdownInput()
close()
setSoLinger(boolean, int)
isOutputShutdown
Since:
1.3/**
     * Disables the output stream for this socket.
     * For a TCP socket, any previously written data will be sent
     * followed by TCP's normal connection termination sequence.
     *
     * If you write to a socket output stream after invoking
     * shutdownOutput() on the socket, the stream will throw
     * an IOException.
     *
     * @exception IOException if an I/O error occurs when shutting down this
     * socket.
     *
     * @since 1.3
     * @see java.net.Socket#shutdownInput()
     * @see java.net.Socket#close()
     * @see java.net.Socket#setSoLinger(boolean, int)
     * @see #isOutputShutdown
     */
    public void shutdownOutput() throws IOException
    {
        if (isClosed())
            throw new SocketException("Socket is closed");
        if (!isConnected())
            throw new SocketException("Socket is not connected");
        if (isOutputShutdown())
            throw new SocketException("Socket output is already shutdown");
        getImpl().shutdownOutput();
        shutOut = true;
    }

    
Converts this socket to a String. 
Returns:
 a string representation of this socket./**
     * Converts this socket to a {@code String}.
     *
     * @return  a string representation of this socket.
     */
    public String toString() {
        try {
            if (isConnected())
                return "Socket[addr=" + getImpl().getInetAddress() +
                    ",port=" + getImpl().getPort() +
                    ",localport=" + getImpl().getLocalPort() + "]";
        } catch (SocketException e) {
        }
        return "Socket[unconnected]";
    }

    
Returns the connection state of the socket.
 Note: Closing a socket doesn't clear its connection state, which means this method will return true for a closed socket (see isClosed()) if it was successfuly connected prior to being closed. 
Returns:
true if the socket was successfuly connected to a server
Since:
1.4/**
     * Returns the connection state of the socket.
     * <p>
     * Note: Closing a socket doesn't clear its connection state, which means
     * this method will return {@code true} for a closed socket
     * (see {@link #isClosed()}) if it was successfuly connected prior
     * to being closed.
     *
     * @return true if the socket was successfuly connected to a server
     * @since 1.4
     */
    public boolean isConnected() {
        // Before 1.3 Sockets were always connected during creation
        return connected || oldImpl;
    }

    
Returns the binding state of the socket.
 Note: Closing a socket doesn't clear its binding state, which means this method will return true for a closed socket (see isClosed()) if it was successfuly bound prior to being closed. 
See Also:
bind
Returns:
true if the socket was successfuly bound to an address
Since:
1.4/**
     * Returns the binding state of the socket.
     * <p>
     * Note: Closing a socket doesn't clear its binding state, which means
     * this method will return {@code true} for a closed socket
     * (see {@link #isClosed()}) if it was successfuly bound prior
     * to being closed.
     *
     * @return true if the socket was successfuly bound to an address
     * @since 1.4
     * @see #bind
     */
    public boolean isBound() {
        // Before 1.3 Sockets were always bound during creation
        return bound || oldImpl;
    }

    
Returns the closed state of the socket.
See Also:
close
Returns:
true if the socket has been closed
Since:
1.4/**
     * Returns the closed state of the socket.
     *
     * @return true if the socket has been closed
     * @since 1.4
     * @see #close
     */
    public boolean isClosed() {
        synchronized(closeLock) {
            return closed;
        }
    }

    
Returns whether the read-half of the socket connection is closed.
See Also:
shutdownInput
Returns:
true if the input of the socket has been shutdown
Since:
1.4/**
     * Returns whether the read-half of the socket connection is closed.
     *
     * @return true if the input of the socket has been shutdown
     * @since 1.4
     * @see #shutdownInput
     */
    public boolean isInputShutdown() {
        return shutIn;
    }

    
Returns whether the write-half of the socket connection is closed.
See Also:
shutdownOutput
Returns:
true if the output of the socket has been shutdown
Since:
1.4/**
     * Returns whether the write-half of the socket connection is closed.
     *
     * @return true if the output of the socket has been shutdown
     * @since 1.4
     * @see #shutdownOutput
     */
    public boolean isOutputShutdown() {
        return shutOut;
    }

    
The factory for all client sockets.
/**
     * The factory for all client sockets.
     */
    private static SocketImplFactory factory = null;

    
Sets the client socket implementation factory for the
application. The factory can be specified only once.
 When an application creates a new client socket, the socket implementation factory's createSocketImpl method is called to create the actual socket implementation. 
 Passing null to the method is a no-op unless the factory was already set. 
If there is a security manager, this method first calls the security manager's checkSetFactory method to ensure the operation is allowed. This could result in a SecurityException. 
Params:
fac –   the desired factory.
Throws:
IOException –  if an I/O error occurs when setting the
              socket factory.
SocketException –  if the factory is already defined.
SecurityException –  if a security manager exists and its checkSetFactory method doesn't allow the operation.
See Also:
SocketImplFactory.createSocketImpl()
SecurityManager.checkSetFactory/**
     * Sets the client socket implementation factory for the
     * application. The factory can be specified only once.
     * <p>
     * When an application creates a new client socket, the socket
     * implementation factory's {@code createSocketImpl} method is
     * called to create the actual socket implementation.
     * <p>
     * Passing {@code null} to the method is a no-op unless the factory
     * was already set.
     * <p>If there is a security manager, this method first calls
     * the security manager's {@code checkSetFactory} method
     * to ensure the operation is allowed.
     * This could result in a SecurityException.
     *
     * @param      fac   the desired factory.
     * @exception  IOException  if an I/O error occurs when setting the
     *               socket factory.
     * @exception  SocketException  if the factory is already defined.
     * @exception  SecurityException  if a security manager exists and its
     *             {@code checkSetFactory} method doesn't allow the operation.
     * @see        java.net.SocketImplFactory#createSocketImpl()
     * @see        SecurityManager#checkSetFactory
     */
    public static synchronized void setSocketImplFactory(SocketImplFactory fac)
        throws IOException
    {
        if (factory != null) {
            throw new SocketException("factory already defined");
        }
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkSetFactory();
        }
        factory = fac;
    }

    
Sets performance preferences for this socket.
 Sockets use the TCP/IP protocol by default.  Some implementations
may offer alternative protocols which have different performance
characteristics than TCP/IP.  This method allows the application to
express its own preferences as to how these tradeoffs should be made
when the implementation chooses from the available protocols.
 Performance preferences are described by three integers whose values indicate the relative importance of short connection time, low latency, and high bandwidth. The absolute values of the integers are irrelevant; in order to choose a protocol the values are simply compared, with larger values indicating stronger preferences. Negative values represent a lower priority than positive values. If the application prefers short connection time over both low latency and high bandwidth, for example, then it could invoke this method with the values (1, 0, 0). If the application prefers high bandwidth above low latency, and low latency above short connection time, then it could invoke this method with the values (0, 1, 2). 
 Invoking this method after this socket has been connected
will have no effect.
Params:
connectionTime –  An int expressing the relative importance of a short connection time
latency –  An int expressing the relative importance of low latency
bandwidth –  An int expressing the relative importance of high bandwidth
Since:
1.5/**
     * Sets performance preferences for this socket.
     *
     * <p> Sockets use the TCP/IP protocol by default.  Some implementations
     * may offer alternative protocols which have different performance
     * characteristics than TCP/IP.  This method allows the application to
     * express its own preferences as to how these tradeoffs should be made
     * when the implementation chooses from the available protocols.
     *
     * <p> Performance preferences are described by three integers
     * whose values indicate the relative importance of short connection time,
     * low latency, and high bandwidth.  The absolute values of the integers
     * are irrelevant; in order to choose a protocol the values are simply
     * compared, with larger values indicating stronger preferences. Negative
     * values represent a lower priority than positive values. If the
     * application prefers short connection time over both low latency and high
     * bandwidth, for example, then it could invoke this method with the values
     * {@code (1, 0, 0)}.  If the application prefers high bandwidth above low
     * latency, and low latency above short connection time, then it could
     * invoke this method with the values {@code (0, 1, 2)}.
     *
     * <p> Invoking this method after this socket has been connected
     * will have no effect.
     *
     * @param  connectionTime
     *         An {@code int} expressing the relative importance of a short
     *         connection time
     *
     * @param  latency
     *         An {@code int} expressing the relative importance of low
     *         latency
     *
     * @param  bandwidth
     *         An {@code int} expressing the relative importance of high
     *         bandwidth
     *
     * @since 1.5
     */
    public void setPerformancePreferences(int connectionTime,
                                          int latency,
                                          int bandwidth)
    {
        /* Not implemented yet */
    }


    
Sets the value of a socket option.
Params:
name – The socket option
value – The value of the socket option. A value of null may be valid for some options.
Type parameters:
<T> – The type of the socket option value
Throws:
UnsupportedOperationException – if the socket does not support
        the option.
IllegalArgumentException – if the value is not valid for
        the option.
IOException – if an I/O error occurs, or if the socket is closed.
NullPointerException – if name is null
SecurityException – if a security manager is set and if the socket option requires a security permission and if the caller does not have the required permission. StandardSocketOptions do not require any security permission.
Returns:
this Socket
Since:
9/**
     * Sets the value of a socket option.
     *
     * @param <T> The type of the socket option value
     * @param name The socket option
     * @param value The value of the socket option. A value of {@code null}
     *              may be valid for some options.
     * @return this Socket
     *
     * @throws UnsupportedOperationException if the socket does not support
     *         the option.
     *
     * @throws IllegalArgumentException if the value is not valid for
     *         the option.
     *
     * @throws IOException if an I/O error occurs, or if the socket is closed.
     *
     * @throws NullPointerException if name is {@code null}
     *
     * @throws SecurityException if a security manager is set and if the socket
     *         option requires a security permission and if the caller does
     *         not have the required permission.
     *         {@link java.net.StandardSocketOptions StandardSocketOptions}
     *         do not require any security permission.
     *
     * @since 9
     */
    public <T> Socket setOption(SocketOption<T> name, T value) throws IOException {
        getImpl().setOption(name, value);
        return this;
    }

    
Returns the value of a socket option.
Params:
name – The socket option
Type parameters:
<T> – The type of the socket option value
Throws:
UnsupportedOperationException – if the socket does not support
        the option.
IOException – if an I/O error occurs, or if the socket is closed.
NullPointerException – if name is null
SecurityException – if a security manager is set and if the socket option requires a security permission and if the caller does not have the required permission. StandardSocketOptions do not require any security permission.
Returns:
The value of the socket option.
Since:
9/**
     * Returns the value of a socket option.
     *
     * @param <T> The type of the socket option value
     * @param name The socket option
     *
     * @return The value of the socket option.
     *
     * @throws UnsupportedOperationException if the socket does not support
     *         the option.
     *
     * @throws IOException if an I/O error occurs, or if the socket is closed.
     *
     * @throws NullPointerException if name is {@code null}
     *
     * @throws SecurityException if a security manager is set and if the socket
     *         option requires a security permission and if the caller does
     *         not have the required permission.
     *         {@link java.net.StandardSocketOptions StandardSocketOptions}
     *         do not require any security permission.
     *
     * @since 9
     */
    @SuppressWarnings("unchecked")
    public <T> T getOption(SocketOption<T> name) throws IOException {
        return getImpl().getOption(name);
    }

    private static Set<SocketOption<?>> options;
    private static boolean optionsSet = false;

    
Returns a set of the socket options supported by this socket.
This method will continue to return the set of options even after
the socket has been closed.
Returns:
A set of the socket options supported by this socket. This set
        may be empty if the socket's SocketImpl cannot be created.
Since:
9/**
     * Returns a set of the socket options supported by this socket.
     *
     * This method will continue to return the set of options even after
     * the socket has been closed.
     *
     * @return A set of the socket options supported by this socket. This set
     *         may be empty if the socket's SocketImpl cannot be created.
     *
     * @since 9
     */
    public Set<SocketOption<?>> supportedOptions() {
        synchronized (Socket.class) {
            if (optionsSet) {
                return options;
            }
            try {
                SocketImpl impl = getImpl();
                options = Collections.unmodifiableSet(impl.supportedOptions());
            } catch (IOException e) {
                options = Collections.emptySet();
            }
            optionsSet = true;
            return options;
        }
    }
}