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package java.lang;

import java.io.*;
import java.util.concurrent.TimeUnit;

The ProcessBuilder.start() and Runtime.exec methods create a native process and return an instance of a subclass of Process that can be used to control the process and obtain information about it. The class Process provides methods for performing input from the process, performing output to the process, waiting for the process to complete, checking the exit status of the process, and destroying (killing) the process. 
The methods that create processes may not work well for special
processes on certain native platforms, such as native windowing
processes, daemon processes, Win16/DOS processes on Microsoft
Windows, or shell scripts.
By default, the created subprocess does not have its own terminal or console. All its standard I/O (i.e. stdin, stdout, stderr) operations will be redirected to the parent process, where they can be accessed via the streams obtained using the methods getOutputStream(), getInputStream(), and getErrorStream(). The parent process uses these streams to feed input to and get output from the subprocess. Because some native platforms only provide limited buffer size for standard input and output streams, failure to promptly write the input stream or read the output stream of the subprocess may cause the subprocess to block, or even deadlock. 
Where desired, 
subprocess I/O can also be redirected using methods of the ProcessBuilder class. 
The subprocess is not killed when there are no more references to the Process object, but rather the subprocess continues executing asynchronously. 
There is no requirement that a process represented by a 
Process object execute asynchronously or concurrently with respect to the Java process that owns the Process object. 
As of 1.5, ProcessBuilder.start() is the preferred way to create a Process. 
Since:
  JDK1.0/**
 * The {@link ProcessBuilder#start()} and
 * {@link Runtime#exec(String[],String[],File) Runtime.exec}
 * methods create a native process and return an instance of a
 * subclass of {@code Process} that can be used to control the process
 * and obtain information about it.  The class {@code Process}
 * provides methods for performing input from the process, performing
 * output to the process, waiting for the process to complete,
 * checking the exit status of the process, and destroying (killing)
 * the process.
 *
 * <p>The methods that create processes may not work well for special
 * processes on certain native platforms, such as native windowing
 * processes, daemon processes, Win16/DOS processes on Microsoft
 * Windows, or shell scripts.
 *
 * <p>By default, the created subprocess does not have its own terminal
 * or console.  All its standard I/O (i.e. stdin, stdout, stderr)
 * operations will be redirected to the parent process, where they can
 * be accessed via the streams obtained using the methods
 * {@link #getOutputStream()},
 * {@link #getInputStream()}, and
 * {@link #getErrorStream()}.
 * The parent process uses these streams to feed input to and get output
 * from the subprocess.  Because some native platforms only provide
 * limited buffer size for standard input and output streams, failure
 * to promptly write the input stream or read the output stream of
 * the subprocess may cause the subprocess to block, or even deadlock.
 *
 * <p>Where desired, <a href="ProcessBuilder.html#redirect-input">
 * subprocess I/O can also be redirected</a>
 * using methods of the {@link ProcessBuilder} class.
 *
 * <p>The subprocess is not killed when there are no more references to
 * the {@code Process} object, but rather the subprocess
 * continues executing asynchronously.
 *
 * <p>There is no requirement that a process represented by a {@code
 * Process} object execute asynchronously or concurrently with respect
 * to the Java process that owns the {@code Process} object.
 *
 * <p>As of 1.5, {@link ProcessBuilder#start()} is the preferred way
 * to create a {@code Process}.
 *
 * @since   JDK1.0
 */
public abstract class Process {
    
Returns the output stream connected to the normal input of the subprocess. Output to the stream is piped into the standard input of the process represented by this Process object. 
If the standard input of the subprocess has been redirected using 
ProcessBuilder.redirectInput then this method will return a null output stream.
Implementation note: It is a good idea for the returned
output stream to be buffered.
Returns:
the output stream connected to the normal input of the
        subprocess/**
     * Returns the output stream connected to the normal input of the
     * subprocess.  Output to the stream is piped into the standard
     * input of the process represented by this {@code Process} object.
     *
     * <p>If the standard input of the subprocess has been redirected using
     * {@link ProcessBuilder#redirectInput(Redirect)
     * ProcessBuilder.redirectInput}
     * then this method will return a
     * <a href="ProcessBuilder.html#redirect-input">null output stream</a>.
     *
     * <p>Implementation note: It is a good idea for the returned
     * output stream to be buffered.
     *
     * @return the output stream connected to the normal input of the
     *         subprocess
     */
    public abstract OutputStream getOutputStream();

    
Returns the input stream connected to the normal output of the subprocess. The stream obtains data piped from the standard output of the process represented by this Process object. 
If the standard output of the subprocess has been redirected using 
ProcessBuilder.redirectOutput then this method will return a null input stream.
Otherwise, if the standard error of the subprocess has been redirected using 
ProcessBuilder.redirectErrorStream then the input stream returned by this method will receive the merged standard output and the standard error of the subprocess. 
Implementation note: It is a good idea for the returned
input stream to be buffered.
Returns:
the input stream connected to the normal output of the
        subprocess/**
     * Returns the input stream connected to the normal output of the
     * subprocess.  The stream obtains data piped from the standard
     * output of the process represented by this {@code Process} object.
     *
     * <p>If the standard output of the subprocess has been redirected using
     * {@link ProcessBuilder#redirectOutput(Redirect)
     * ProcessBuilder.redirectOutput}
     * then this method will return a
     * <a href="ProcessBuilder.html#redirect-output">null input stream</a>.
     *
     * <p>Otherwise, if the standard error of the subprocess has been
     * redirected using
     * {@link ProcessBuilder#redirectErrorStream(boolean)
     * ProcessBuilder.redirectErrorStream}
     * then the input stream returned by this method will receive the
     * merged standard output and the standard error of the subprocess.
     *
     * <p>Implementation note: It is a good idea for the returned
     * input stream to be buffered.
     *
     * @return the input stream connected to the normal output of the
     *         subprocess
     */
    public abstract InputStream getInputStream();

    
Returns the input stream connected to the error output of the subprocess. The stream obtains data piped from the error output of the process represented by this Process object. 
If the standard error of the subprocess has been redirected using 
ProcessBuilder.redirectError or 
ProcessBuilder.redirectErrorStream then this method will return a null input stream.
Implementation note: It is a good idea for the returned
input stream to be buffered.
Returns:
the input stream connected to the error output of
        the subprocess/**
     * Returns the input stream connected to the error output of the
     * subprocess.  The stream obtains data piped from the error output
     * of the process represented by this {@code Process} object.
     *
     * <p>If the standard error of the subprocess has been redirected using
     * {@link ProcessBuilder#redirectError(Redirect)
     * ProcessBuilder.redirectError} or
     * {@link ProcessBuilder#redirectErrorStream(boolean)
     * ProcessBuilder.redirectErrorStream}
     * then this method will return a
     * <a href="ProcessBuilder.html#redirect-output">null input stream</a>.
     *
     * <p>Implementation note: It is a good idea for the returned
     * input stream to be buffered.
     *
     * @return the input stream connected to the error output of
     *         the subprocess
     */
    public abstract InputStream getErrorStream();

    
Causes the current thread to wait, if necessary, until the process represented by this Process object has terminated. This method returns immediately if the subprocess has already terminated. If the subprocess has not yet terminated, the calling thread will be blocked until the subprocess exits. 
Throws:
InterruptedException – if the current thread is interrupted by another thread while it is waiting, then the wait is ended and an InterruptedException is thrown.
Returns:
the exit value of the subprocess represented by this Process object. By convention, the value 0 indicates normal termination./**
     * Causes the current thread to wait, if necessary, until the
     * process represented by this {@code Process} object has
     * terminated.  This method returns immediately if the subprocess
     * has already terminated.  If the subprocess has not yet
     * terminated, the calling thread will be blocked until the
     * subprocess exits.
     *
     * @return the exit value of the subprocess represented by this
     *         {@code Process} object.  By convention, the value
     *         {@code 0} indicates normal termination.
     * @throws InterruptedException if the current thread is
     *         {@linkplain Thread#interrupt() interrupted} by another
     *         thread while it is waiting, then the wait is ended and
     *         an {@link InterruptedException} is thrown.
     */
    public abstract int waitFor() throws InterruptedException;

    
Causes the current thread to wait, if necessary, until the subprocess represented by this Process object has terminated, or the specified waiting time elapses. 
If the subprocess has already terminated then this method returns immediately with the value true. If the process has not terminated and the timeout value is less than, or equal to, zero, then this method returns immediately with the value false. 
The default implementation of this methods polls the exitValue to check if the process has terminated. Concrete implementations of this class are strongly encouraged to override this method with a more efficient implementation. 
Params:
timeout – the maximum time to wait
unit – the time unit of the timeout argument
Throws:
InterruptedException – if the current thread is interrupted
        while waiting.
NullPointerException – if unit is null
Returns:
true if the subprocess has exited and false if the waiting time elapsed before the subprocess has exited.
Since:
1.8/**
     * Causes the current thread to wait, if necessary, until the
     * subprocess represented by this {@code Process} object has
     * terminated, or the specified waiting time elapses.
     *
     * <p>If the subprocess has already terminated then this method returns
     * immediately with the value {@code true}.  If the process has not
     * terminated and the timeout value is less than, or equal to, zero, then
     * this method returns immediately with the value {@code false}.
     *
     * <p>The default implementation of this methods polls the {@code exitValue}
     * to check if the process has terminated. Concrete implementations of this
     * class are strongly encouraged to override this method with a more
     * efficient implementation.
     *
     * @param timeout the maximum time to wait
     * @param unit the time unit of the {@code timeout} argument
     * @return {@code true} if the subprocess has exited and {@code false} if
     *         the waiting time elapsed before the subprocess has exited.
     * @throws InterruptedException if the current thread is interrupted
     *         while waiting.
     * @throws NullPointerException if unit is null
     * @since 1.8
     */
    public boolean waitFor(long timeout, TimeUnit unit)
        throws InterruptedException
    {
        long startTime = System.nanoTime();
        long rem = unit.toNanos(timeout);

        do {
            try {
                exitValue();
                return true;
            } catch(IllegalThreadStateException ex) {
                if (rem > 0)
                    Thread.sleep(
                        Math.min(TimeUnit.NANOSECONDS.toMillis(rem) + 1, 100));
            }
            rem = unit.toNanos(timeout) - (System.nanoTime() - startTime);
        } while (rem > 0);
        return false;
    }

    
Returns the exit value for the subprocess.
Throws:
IllegalThreadStateException – if the subprocess represented by this Process object has not yet terminated
Returns:
the exit value of the subprocess represented by this Process object. By convention, the value 0 indicates normal termination./**
     * Returns the exit value for the subprocess.
     *
     * @return the exit value of the subprocess represented by this
     *         {@code Process} object.  By convention, the value
     *         {@code 0} indicates normal termination.
     * @throws IllegalThreadStateException if the subprocess represented
     *         by this {@code Process} object has not yet terminated
     */
    public abstract int exitValue();

    
Kills the subprocess. Whether the subprocess represented by this Process object is forcibly terminated or not is implementation dependent. /**
     * Kills the subprocess. Whether the subprocess represented by this
     * {@code Process} object is forcibly terminated or not is
     * implementation dependent.
     */
    public abstract void destroy();

    
Kills the subprocess. The subprocess represented by this Process object is forcibly terminated. 
The default implementation of this method invokes destroy and so may not forcibly terminate the process. Concrete implementations of this class are strongly encouraged to override this method with a compliant implementation. Invoking this method on Process objects returned by ProcessBuilder.start and Runtime.exec will forcibly terminate the process. 
Note: The subprocess may not terminate immediately. i.e. isAlive() may return true for a brief period after destroyForcibly() is called. This method may be chained to waitFor() if needed. 
Returns:
the Process object representing the subprocess to be forcibly destroyed.
Since:
1.8/**
     * Kills the subprocess. The subprocess represented by this
     * {@code Process} object is forcibly terminated.
     *
     * <p>The default implementation of this method invokes {@link #destroy}
     * and so may not forcibly terminate the process. Concrete implementations
     * of this class are strongly encouraged to override this method with a
     * compliant implementation.  Invoking this method on {@code Process}
     * objects returned by {@link ProcessBuilder#start} and
     * {@link Runtime#exec} will forcibly terminate the process.
     *
     * <p>Note: The subprocess may not terminate immediately.
     * i.e. {@code isAlive()} may return true for a brief period
     * after {@code destroyForcibly()} is called. This method
     * may be chained to {@code waitFor()} if needed.
     *
     * @return the {@code Process} object representing the
     *         subprocess to be forcibly destroyed.
     * @since 1.8
     */
    public Process destroyForcibly() {
        destroy();
        return this;
    }

    
Tests whether the subprocess represented by this Process is alive. 
Returns:
true if the subprocess represented by this Process object has not yet terminated.
Since:
1.8/**
     * Tests whether the subprocess represented by this {@code Process} is
     * alive.
     *
     * @return {@code true} if the subprocess represented by this
     *         {@code Process} object has not yet terminated.
     * @since 1.8
     */
    public boolean isAlive() {
        try {
            exitValue();
            return false;
        } catch(IllegalThreadStateException e) {
            return true;
        }
    }
}