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package com.sun.tools.attach;

import com.sun.tools.attach.spi.AttachProvider;

Describes a Java virtual machine.
 A VirtualMachineDescriptor is a container class used to describe a Java virtual machine. It encapsulates an identifier that identifies a target virtual machine, and a reference to the AttachProvider that should be used when attempting to attach to the virtual machine. The identifier is implementation-dependent but is typically the process identifier (or pid) environments where each Java virtual machine runs in its own operating system process. 
 A VirtualMachineDescriptor also has a displayName. The display name is typically a human readable string that a tool might display to a user. For example, a tool that shows a list of Java virtual machines running on a system might use the display name rather than the identifier. A VirtualMachineDescriptor may be
created without a display name. In that case the identifier is
used as the display name.
 VirtualMachineDescriptor instances are typically created by invoking the VirtualMachine.list() method. This returns the complete list of descriptors to describe the Java virtual machines known to all installed attach providers. 
Since:
1.6/**
 * Describes a Java virtual machine.
 *
 * <p> A <code>VirtualMachineDescriptor</code> is a container class used to
 * describe a Java virtual machine. It encapsulates an identifier that identifies
 * a target virtual machine, and a reference to the {@link
 * com.sun.tools.attach.spi.AttachProvider AttachProvider} that should be used
 * when attempting to attach to the virtual machine. The identifier is
 * implementation-dependent but is typically the process identifier (or pid)
 * environments where each Java virtual machine runs in its own operating system
 * process. </p>
 *
 * <p> A <code>VirtualMachineDescriptor</code> also has a {@link #displayName() displayName}.
 * The display name is typically a human readable string that a tool might
 * display to a user. For example, a tool that shows a list of Java
 * virtual machines running on a system might use the display name rather
 * than the identifier. A <code>VirtualMachineDescriptor</code> may be
 * created without a <i>display name</i>. In that case the identifier is
 * used as the <i>display name</i>.
 *
 * <p> <code>VirtualMachineDescriptor</code> instances are typically created by
 * invoking the {@link com.sun.tools.attach.VirtualMachine#list VirtualMachine.list()}
 * method. This returns the complete list of descriptors to describe the
 * Java virtual machines known to all installed {@link
 * com.sun.tools.attach.spi.AttachProvider attach providers}.
 *
 * @since 1.6
 */
public class VirtualMachineDescriptor {

    private AttachProvider provider;
    private String id;
    private String displayName;

    private volatile int hash;        // 0 => not computed

    
Creates a virtual machine descriptor from the given components.
Params:
provider –      The AttachProvider to attach to the Java virtual machine.
id –            The virtual machine identifier.
displayName –   The display name.
Throws:
NullPointerException – 
         If any of the arguments are null/**
     * Creates a virtual machine descriptor from the given components.
     *
     * @param   provider      The AttachProvider to attach to the Java virtual machine.
     * @param   id            The virtual machine identifier.
     * @param   displayName   The display name.
     *
     * @throws  NullPointerException
     *          If any of the arguments are <code>null</code>
     */
    public VirtualMachineDescriptor(AttachProvider provider, String id, String displayName) {
        if (provider == null) {
            throw new NullPointerException("provider cannot be null");
        }
        if (id == null) {
            throw new NullPointerException("identifier cannot be null");
        }
        if (displayName == null) {
            throw new NullPointerException("display name cannot be null");
        }
        this.provider = provider;
        this.id = id;
        this.displayName = displayName;
    }

    
Creates a virtual machine descriptor from the given components.
 This convenience constructor works as if by invoking the
three-argument constructor as follows:
 new 
VirtualMachineDescriptor(provider, id, id); 
 That is, it creates a virtual machine descriptor such that
the display name is the same as the virtual machine
identifier.
Params:
provider –      The AttachProvider to attach to the Java virtual machine.
id –            The virtual machine identifier.
Throws:
NullPointerException – 
         If provider or id is null./**
     * Creates a virtual machine descriptor from the given components.
     *
     * <p> This convenience constructor works as if by invoking the
     * three-argument constructor as follows:
     *
     * <blockquote><tt>
     * new&nbsp;{@link #VirtualMachineDescriptor(AttachProvider, String, String)
     * VirtualMachineDescriptor}(provider, &nbsp;id, &nbsp;id);
     * </tt></blockquote>
     *
     * <p> That is, it creates a virtual machine descriptor such that
     * the <i>display name</i> is the same as the virtual machine
     * identifier.
     *
     * @param   provider      The AttachProvider to attach to the Java virtual machine.
     * @param   id            The virtual machine identifier.
     *
     * @throws  NullPointerException
     *          If <tt>provider</tt> or <tt>id</tt> is <tt>null</tt>.
     */
    public VirtualMachineDescriptor(AttachProvider provider, String id) {
        this(provider, id, id);
    }

    
Return the AttachProvider that this descriptor references.
Returns:
The AttachProvider that this descriptor references./**
     * Return the <code>AttachProvider</code> that this descriptor references.
     *
     * @return The <code>AttachProvider</code> that this descriptor references.
     */
    public AttachProvider provider() {
        return provider;
    }

    
Return the identifier component of this descriptor.
Returns:
 The identifier component of this descriptor./**
     * Return the identifier component of this descriptor.
     *
     * @return  The identifier component of this descriptor.
     */
    public String id() {
        return id;
    }

    
Return the display name component of this descriptor.
Returns:
 The display name component of this descriptor./**
     * Return the <i>display name</i> component of this descriptor.
     *
     * @return  The display name component of this descriptor.
     */
    public String displayName() {
        return displayName;
    }

    
Returns a hash-code value for this VirtualMachineDescriptor. The hash code is based upon the descriptor's components, and satifies the general contract of the 
Object.hashCode method. 
Returns:
 A hash-code value for this descriptor./**
     * Returns a hash-code value for this VirtualMachineDescriptor. The hash
     * code is based upon the descriptor's components, and satifies
     * the general contract of the {@link java.lang.Object#hashCode()
     * Object.hashCode} method.
     *
     * @return  A hash-code value for this descriptor.
     */
    public int hashCode() {
        if (hash != 0) {
            return hash;
        }
        hash = provider.hashCode() * 127 + id.hashCode();
        return hash;
    }

    
Tests this VirtualMachineDescriptor for equality with another object.
 If the given object is not a VirtualMachineDescriptor then this
method returns false. For two VirtualMachineDescriptors to be considered equal requires that they both reference the same provider, and their identifiers are equal. 
 This method satisfies the general contract of the Object.equals method. 
Params:
ob –   The object to which this object is to be compared
Returns:
 true if, and only if, the given object is
               a VirtualMachineDescriptor that is equal to this
               VirtualMachineDescriptor./**
     * Tests this VirtualMachineDescriptor for equality with another object.
     *
     * <p> If the given object is not a VirtualMachineDescriptor then this
     * method returns <tt>false</tt>. For two VirtualMachineDescriptors to
     * be considered equal requires that they both reference the same
     * provider, and their {@link #id() identifiers} are equal. </p>
     *
     * <p> This method satisfies the general contract of the {@link
     * java.lang.Object#equals(Object) Object.equals} method. </p>
     *
     * @param   ob   The object to which this object is to be compared
     *
     * @return  <tt>true</tt> if, and only if, the given object is
     *                a VirtualMachineDescriptor that is equal to this
     *                VirtualMachineDescriptor.
     */
    public boolean equals(Object ob) {
        if (ob == this)
            return true;
        if (!(ob instanceof VirtualMachineDescriptor))
            return false;
        VirtualMachineDescriptor other = (VirtualMachineDescriptor)ob;
        if (other.provider() != this.provider()) {
            return false;
        }
        if (!other.id().equals(this.id())) {
            return false;
        }
        return true;
    }

    
Returns the string representation of the VirtualMachineDescriptor.
/**
     * Returns the string representation of the <code>VirtualMachineDescriptor</code>.
     */
    public String toString() {
        String s = provider.toString() + ": " + id;
        if (displayName != id) {
            s += " " + displayName;
        }
        return s;
    }


}