/*

 * Copyright (c) 2005, 2013, 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 com.sun.tools.attach;

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

/**

 * Describes a Java virtual machine.

 *

 * <p> A {@code 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 {@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} 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} 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} 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.

     *

     * @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}

     */

    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.

     *

     * <p> This convenience constructor works as if by invoking the

     * three-argument constructor as follows:

     *

     * <blockquote><code>

     * new {@link #VirtualMachineDescriptor(AttachProvider, String, String)

     * VirtualMachineDescriptor}(provider,  id,  id);

     * </code></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 {@code provider} or {@code id} is {@code null}.

     */

    public VirtualMachineDescriptor(AttachProvider provider, String id) {

        this(provider, id, id);

    }

    /**

     * Return the {@code AttachProvider} that this descriptor references.

     *

     * @return The {@code AttachProvider} that this descriptor references.

     */

    public AttachProvider provider() {

        return provider;

    }

    /**

     * Return the identifier component of this descriptor.

     *

     * @return  The identifier component of this descriptor.

     */

    public String id() {

        return id;

    }

    /**

     * 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 {@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.

     *

     * <p> If the given object is not a VirtualMachineDescriptor then this

     * method returns {@code false}. 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  {@code true} 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 {@code VirtualMachineDescriptor}.

     */

    public String toString() {

        String s = provider.toString() + ": " + id;

        if (displayName != id) {

            s += " " + displayName;

        }

        return s;

    }

}