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	/*
	* Copyright (c) 2005, 2014, 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
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package com.sun.tools.attach;

	import com.sun.tools.attach.spi.AttachProvider;
	import java.util.ArrayList;
	import java.util.List;
	import java.util.Properties;
	import java.io.IOException;


	/**
	* A Java virtual machine.
	*
	* <p> A <code>VirtualMachine</code> represents a Java virtual machine to which this
	* Java virtual machine has attached. The Java virtual machine to which it is
	* attached is sometimes called the <i>target virtual machine</i>, or <i>target VM</i>.
	* An application (typically a tool such as a managemet console or profiler) uses a
	* VirtualMachine to load an agent into the target VM. For example, a profiler tool
	* written in the Java Language might attach to a running application and load its
	* profiler agent to profile the running application. </p>
	*
	* <p> A VirtualMachine is obtained by invoking the {@link #attach(String) attach} method
	* with an identifier that identifies the target virtual machine. The identifier is
	* implementation-dependent but is typically the process identifier (or pid) in
	* environments where each Java virtual machine runs in its own operating system process.
	* Alternatively, a <code>VirtualMachine</code> instance is obtained by invoking the
	* {@link #attach(VirtualMachineDescriptor) attach} method with a {@link
	* com.sun.tools.attach.VirtualMachineDescriptor VirtualMachineDescriptor} obtained
	* from the list of virtual machine descriptors returned by the {@link #list list} method.
	* Once a reference to a virtual machine is obtained, the {@link #loadAgent loadAgent},
	* {@link #loadAgentLibrary loadAgentLibrary}, and {@link #loadAgentPath loadAgentPath}
	* methods are used to load agents into target virtual machine. The {@link
	* #loadAgent loadAgent} method is used to load agents that are written in the Java
	* Language and deployed in a {@link java.util.jar.JarFile JAR file}. (See
	* {@link java.lang.instrument} for a detailed description on how these agents
	* are loaded and started). The {@link #loadAgentLibrary loadAgentLibrary} and
	* {@link #loadAgentPath loadAgentPath} methods are used to load agents that
	* are deployed either in a dynamic library or statically linked into the VM and make use of the <a
	* href="../../../../../../../../technotes/guides/jvmti/index.html">JVM Tools
	* Interface</a>. </p>
	*
	* <p> In addition to loading agents a VirtualMachine provides read access to the
	* {@link java.lang.System#getProperties() system properties} in the target VM.
	* This can be useful in some environments where properties such as
	* <code>java.home</code>, <code>os.name</code>, or <code>os.arch</code> are
	* used to construct the path to agent that will be loaded into the target VM.
	*
	* <p> The following example demonstrates how VirtualMachine may be used:</p>
	*
	* <pre>
	*
	* // attach to target VM
	* VirtualMachine vm = VirtualMachine.attach("2177");
	*
	* // start management agent
	* Properties props = new Properties();
	* props.put("com.sun.management.jmxremote.port", "5000");
	* vm.startManagementAgent(props);
	*
	* // detach
	* vm.detach();
	*
	* </pre>
	*
	* <p> In this example we attach to a Java virtual machine that is identified by
	* the process identifier <code>2177</code>. Then the JMX management agent is
	* started in the target process using the supplied arguments. Finally, the
	* client detaches from the target VM. </p>
	*
	* <p> A VirtualMachine is safe for use by multiple concurrent threads. </p>
	*
	* @since 1.6
	*/

	@jdk.Exported
	public abstract class VirtualMachine {
	private AttachProvider provider;
	private String id;
	private volatile int hash; // 0 => not computed

	/**
	* Initializes a new instance of this class.
	*
	* @param provider
	* The attach provider creating this class.
	* @param id
	* The abstract identifier that identifies the Java virtual machine.
	*
	* @throws NullPointerException
	* If <code>provider</code> or <code>id</code> is <code>null</code>.
	*/
	protected VirtualMachine(AttachProvider provider, String id) {
	if (provider == null) {
	throw new NullPointerException("provider cannot be null");
	}
	if (id == null) {
	throw new NullPointerException("id cannot be null");
	}
	this.provider = provider;
	this.id = id;
	}

	/**
	* Return a list of Java virtual machines.
	*
	* <p> This method returns a list of Java {@link
	* com.sun.tools.attach.VirtualMachineDescriptor} elements.
	* The list is an aggregation of the virtual machine
	* descriptor lists obtained by invoking the {@link
	* com.sun.tools.attach.spi.AttachProvider#listVirtualMachines
	* listVirtualMachines} method of all installed
	* {@link com.sun.tools.attach.spi.AttachProvider attach providers}.
	* If there are no Java virtual machines known to any provider
	* then an empty list is returned.
	*
	* @return The list of virtual machine descriptors.
	*/
	public static List<VirtualMachineDescriptor> list() {
	ArrayList<VirtualMachineDescriptor> l =
	new ArrayList<VirtualMachineDescriptor>();
	List<AttachProvider> providers = AttachProvider.providers();
	for (AttachProvider provider: providers) {
	l.addAll(provider.listVirtualMachines());
	}
	return l;
	}

	/**
	* Attaches to a Java virtual machine.
	*
	* <p> This method obtains the list of attach providers by invoking the
	* {@link com.sun.tools.attach.spi.AttachProvider#providers()
	* AttachProvider.providers()} method. It then iterates overs the list
	* and invokes each provider's {@link
	* com.sun.tools.attach.spi.AttachProvider#attachVirtualMachine(java.lang.String)
	* attachVirtualMachine} method in turn. If a provider successfully
	* attaches then the iteration terminates, and the VirtualMachine created
	* by the provider that successfully attached is returned by this method.
	* If the <code>attachVirtualMachine</code> method of all providers throws
	* {@link com.sun.tools.attach.AttachNotSupportedException AttachNotSupportedException}
	* then this method also throws <code>AttachNotSupportedException</code>.
	* This means that <code>AttachNotSupportedException</code> is thrown when
	* the identifier provided to this method is invalid, or the identifier
	* corresponds to a Java virtual machine that does not exist, or none
	* of the providers can attach to it. This exception is also thrown if
	* {@link com.sun.tools.attach.spi.AttachProvider#providers()
	* AttachProvider.providers()} returns an empty list. </p>
	*
	* @param id
	* The abstract identifier that identifies the Java virtual machine.
	*
	* @return A VirtualMachine representing the target VM.
	*
	* @throws SecurityException
	* If a security manager has been installed and it denies
	* {@link com.sun.tools.attach.AttachPermission AttachPermission}
	* <tt>("attachVirtualMachine")</tt>, or another permission
	* required by the implementation.
	*
	* @throws AttachNotSupportedException
	* If the <code>attachVirtualmachine</code> method of all installed
	* providers throws <code>AttachNotSupportedException</code>, or
	* there aren't any providers installed.
	*
	* @throws IOException
	* If an I/O error occurs
	*
	* @throws NullPointerException
	* If <code>id</code> is <code>null</code>.
	*/
	public static VirtualMachine attach(String id)
	throws AttachNotSupportedException, IOException
	{
	if (id == null) {
	throw new NullPointerException("id cannot be null");
	}
	List<AttachProvider> providers = AttachProvider.providers();
	if (providers.size() == 0) {
	throw new AttachNotSupportedException("no providers installed");
	}
	AttachNotSupportedException lastExc = null;
	for (AttachProvider provider: providers) {
	try {
	return provider.attachVirtualMachine(id);
	} catch (AttachNotSupportedException x) {
	lastExc = x;
	}
	}
	throw lastExc;
	}

	/**
	* Attaches to a Java virtual machine.
	*
	* <p> This method first invokes the {@link
	* com.sun.tools.attach.VirtualMachineDescriptor#provider() provider()} method
	* of the given virtual machine descriptor to obtain the attach provider. It
	* then invokes the attach provider's {@link
	* com.sun.tools.attach.spi.AttachProvider#attachVirtualMachine(VirtualMachineDescriptor)
	* attachVirtualMachine} to attach to the target VM.
	*
	* @param vmd
	* The virtual machine descriptor.
	*
	* @return A VirtualMachine representing the target VM.
	*
	* @throws SecurityException
	* If a security manager has been installed and it denies
	* {@link com.sun.tools.attach.AttachPermission AttachPermission}
	* <tt>("attachVirtualMachine")</tt>, or another permission
	* required by the implementation.
	*
	* @throws AttachNotSupportedException
	* If the attach provider's <code>attachVirtualmachine</code>
	* throws <code>AttachNotSupportedException</code>.
	*
	* @throws IOException
	* If an I/O error occurs
	*
	* @throws NullPointerException
	* If <code>vmd</code> is <code>null</code>.
	*/
	public static VirtualMachine attach(VirtualMachineDescriptor vmd)
	throws AttachNotSupportedException, IOException
	{
	return vmd.provider().attachVirtualMachine(vmd);
	}

	/**
	* Detach from the virtual machine.
	*
	* <p> After detaching from the virtual machine, any further attempt to invoke
	* operations on that virtual machine will cause an {@link java.io.IOException
	* IOException} to be thrown. If an operation (such as {@link #loadAgent
	* loadAgent} for example) is in progress when this method is invoked then
	* the behaviour is implementation dependent. In other words, it is
	* implementation specific if the operation completes or throws
	* <tt>IOException</tt>.
	*
	* <p> If already detached from the virtual machine then invoking this
	* method has no effect. </p>
	*
	* @throws IOException
	* If an I/O error occurs
	*/
	public abstract void detach() throws IOException;

	/**
	* Returns the provider that created this virtual machine.
	*
	* @return The provider that created this virtual machine.
	*/
	public final AttachProvider provider() {
	return provider;
	}

	/**
	* Returns the identifier for this Java virtual machine.
	*
	* @return The identifier for this Java virtual machine.
	*/
	public final String id() {
	return id;
	}

	/**
	* Loads an agent library.
	*
	* <p> A <a href="../../../../../../../../technotes/guides/jvmti/index.html">JVM
	* TI</a> client is called an <i>agent</i>. It is developed in a native language.
	* A JVM TI agent is deployed in a platform specific manner but it is typically the
	* platform equivalent of a dynamic library. Alternatively, it may be statically linked into the VM.
	* This method causes the given agent library to be loaded into the target
	* VM (if not already loaded or if not statically linked into the VM).
	* It then causes the target VM to invoke the <code>Agent_OnAttach</code> function
	* or, for a statically linked agent named 'L', the <code>Agent_OnAttach_L</code> function
	* as specified in the
	* <a href="../../../../../../../../technotes/guides/jvmti/index.html"> JVM Tools
	* Interface</a> specification. Note that the <code>Agent_OnAttach[_L]</code>
	* function is invoked even if the agent library was loaded prior to invoking
	* this method.
	*
	* <p> The agent library provided is the name of the agent library. It is interpreted
	* in the target virtual machine in an implementation-dependent manner. Typically an
	* implementation will expand the library name into an operating system specific file
	* name. For example, on UNIX systems, the name <tt>L</tt> might be expanded to
	* <tt>libL.so</tt>, and located using the search path specified by the
	* <tt>LD_LIBRARY_PATH</tt> environment variable. If the agent named 'L' is
	* statically linked into the VM then the VM must export a function named
	* <code>Agent_OnAttach_L</code>.</p>
	*
	* <p> If the <code>Agent_OnAttach[_L]</code> function in the agent library returns
	* an error then an {@link com.sun.tools.attach.AgentInitializationException} is
	* thrown. The return value from the <code>Agent_OnAttach[_L]</code> can then be
	* obtained by invoking the {@link
	* com.sun.tools.attach.AgentInitializationException#returnValue() returnValue}
	* method on the exception. </p>
	*
	* @param agentLibrary
	* The name of the agent library.
	*
	* @param options
	* The options to provide to the <code>Agent_OnAttach[_L]</code>
	* function (can be <code>null</code>).
	*
	* @throws AgentLoadException
	* If the agent library does not exist, the agent library is not
	* statically linked with the VM, or the agent library cannot be
	* loaded for another reason.
	*
	* @throws AgentInitializationException
	* If the <code>Agent_OnAttach[_L]</code> function returns an error.
	*
	* @throws IOException
	* If an I/O error occurs
	*
	* @throws NullPointerException
	* If <code>agentLibrary</code> is <code>null</code>.
	*
	* @see com.sun.tools.attach.AgentInitializationException#returnValue()
	*/
	public abstract void loadAgentLibrary(String agentLibrary, String options)
	throws AgentLoadException, AgentInitializationException, IOException;

	/**
	* Loads an agent library.
	*
	* <p> This convenience method works as if by invoking:
	*
	* <blockquote><tt>
	* {@link #loadAgentLibrary(String, String) loadAgentLibrary}(agentLibrary, null);
	* </tt></blockquote>
	*
	* @param agentLibrary
	* The name of the agent library.
	*
	* @throws AgentLoadException
	* If the agent library does not exist, the agent library is not
	* statically linked with the VM, or the agent library cannot be
	* loaded for another reason.
	*
	* @throws AgentInitializationException
	* If the <code>Agent_OnAttach[_L]</code> function returns an error.
	*
	* @throws IOException
	* If an I/O error occurs
	*
	* @throws NullPointerException
	* If <code>agentLibrary</code> is <code>null</code>.
	*/
	public void loadAgentLibrary(String agentLibrary)
	throws AgentLoadException, AgentInitializationException, IOException
	{
	loadAgentLibrary(agentLibrary, null);
	}

	/**
	* Load a native agent library by full pathname.
	*
	* <p> A <a href="../../../../../../../../technotes/guides/jvmti/index.html">JVM
	* TI</a> client is called an <i>agent</i>. It is developed in a native language.
	* A JVM TI agent is deployed in a platform specific manner but it is typically the
	* platform equivalent of a dynamic library. Alternatively, the native
	* library specified by the agentPath parameter may be statically
	* linked with the VM. The parsing of the agentPath parameter into
	* a statically linked library name is done in a platform
	* specific manner in the VM. For example, in UNIX, an agentPath parameter
	* of <code>/a/b/libL.so</code> would name a library 'L'.
	*
	* See the JVM TI Specification for more details.
	*
	* This method causes the given agent library to be loaded into the target
	* VM (if not already loaded or if not statically linked into the VM).
	* It then causes the target VM to invoke the <code>Agent_OnAttach</code>
	* function or, for a statically linked agent named 'L', the
	* <code>Agent_OnAttach_L</code> function as specified in the
	* <a href="../../../../../../../../technotes/guides/jvmti/index.html"> JVM Tools
	* Interface</a> specification.
	* Note that the <code>Agent_OnAttach[_L]</code>
	* function is invoked even if the agent library was loaded prior to invoking
	* this method.
	*
	* <p> The agent library provided is the absolute path from which to load the
	* agent library. Unlike {@link #loadAgentLibrary loadAgentLibrary}, the library name
	* is not expanded in the target virtual machine. </p>
	*
	* <p> If the <code>Agent_OnAttach[_L]</code> function in the agent library returns
	* an error then an {@link com.sun.tools.attach.AgentInitializationException} is
	* thrown. The return value from the <code>Agent_OnAttach[_L]</code> can then be
	* obtained by invoking the {@link
	* com.sun.tools.attach.AgentInitializationException#returnValue() returnValue}
	* method on the exception. </p>
	*
	* @param agentPath
	* The full path of the agent library.
	*
	* @param options
	* The options to provide to the <code>Agent_OnAttach[_L]</code>
	* function (can be <code>null</code>).
	*
	* @throws AgentLoadException
	* If the agent library does not exist, the agent library is not
	* statically linked with the VM, or the agent library cannot be
	* loaded for another reason.
	*
	* @throws AgentInitializationException
	* If the <code>Agent_OnAttach[_L]</code> function returns an error.
	*
	* @throws IOException
	* If an I/O error occurs
	*
	* @throws NullPointerException
	* If <code>agentPath</code> is <code>null</code>.
	*
	* @see com.sun.tools.attach.AgentInitializationException#returnValue()
	*/
	public abstract void loadAgentPath(String agentPath, String options)
	throws AgentLoadException, AgentInitializationException, IOException;

	/**
	* Load a native agent library by full pathname.
	*
	* <p> This convenience method works as if by invoking:
	*
	* <blockquote><tt>
	* {@link #loadAgentPath(String, String) loadAgentPath}(agentLibrary, null);
	* </tt></blockquote>
	*
	* @param agentPath
	* The full path to the agent library.
	*
	* @throws AgentLoadException
	* If the agent library does not exist, the agent library is not
	* statically linked with the VM, or the agent library cannot be
	* loaded for another reason.
	*
	* @throws AgentInitializationException
	* If the <code>Agent_OnAttach[_L]</code> function returns an error.
	*
	* @throws IOException
	* If an I/O error occurs
	*
	* @throws NullPointerException
	* If <code>agentPath</code> is <code>null</code>.
	*/
	public void loadAgentPath(String agentPath)
	throws AgentLoadException, AgentInitializationException, IOException
	{
	loadAgentPath(agentPath, null);
	}


	/**
	* Loads an agent.
	*
	* <p> The agent provided to this method is a path name to a JAR file on the file
	* system of the target virtual machine. This path is passed to the target virtual
	* machine where it is interpreted. The target virtual machine attempts to start
	* the agent as specified by the {@link java.lang.instrument} specification.
	* That is, the specified JAR file is added to the system class path (of the target
	* virtual machine), and the <code>agentmain</code> method of the agent class, specified
	* by the <code>Agent-Class</code> attribute in the JAR manifest, is invoked. This
	* method completes when the <code>agentmain</code> method completes.
	*
	* @param agent
	* Path to the JAR file containing the agent.
	*
	* @param options
	* The options to provide to the agent's <code>agentmain</code>
	* method (can be <code>null</code>).
	*
	* @throws AgentLoadException
	* If the agent does not exist, or cannot be started in the manner
	* specified in the {@link java.lang.instrument} specification.
	*
	* @throws AgentInitializationException
	* If the <code>agentmain</code> throws an exception
	*
	* @throws IOException
	* If an I/O error occurs
	*
	* @throws NullPointerException
	* If <code>agent</code> is <code>null</code>.
	*/
	public abstract void loadAgent(String agent, String options)
	throws AgentLoadException, AgentInitializationException, IOException;

	/**
	* Loads an agent.
	*
	* <p> This convenience method works as if by invoking:
	*
	* <blockquote><tt>
	* {@link #loadAgent(String, String) loadAgent}(agent, null);
	* </tt></blockquote>
	*
	* @param agent
	* Path to the JAR file containing the agent.
	*
	* @throws AgentLoadException
	* If the agent does not exist, or cannot be started in the manner
	* specified in the {@link java.lang.instrument} specification.
	*
	* @throws AgentInitializationException
	* If the <code>agentmain</code> throws an exception
	*
	* @throws IOException
	* If an I/O error occurs
	*
	* @throws NullPointerException
	* If <code>agent</code> is <code>null</code>.
	*/
	public void loadAgent(String agent)
	throws AgentLoadException, AgentInitializationException, IOException
	{
	loadAgent(agent, null);
	}

	/**
	* Returns the current system properties in the target virtual machine.
	*
	* <p> This method returns the system properties in the target virtual
	* machine. Properties whose key or value is not a <tt>String</tt> are
	* omitted. The method is approximately equivalent to the invocation of the
	* method {@link java.lang.System#getProperties System.getProperties}
	* in the target virtual machine except that properties with a key or
	* value that is not a <tt>String</tt> are not included.
	*
	* <p> This method is typically used to decide which agent to load into
	* the target virtual machine with {@link #loadAgent loadAgent}, or
	* {@link #loadAgentLibrary loadAgentLibrary}. For example, the
	* <code>java.home</code> or <code>user.dir</code> properties might be
	* use to create the path to the agent library or JAR file.
	*
	* @return The system properties
	*
	* @throws AttachOperationFailedException
	* If the target virtual machine is unable to complete the
	* attach operation. A more specific error message will be
	* given by {@link AttachOperationFailedException#getMessage()}.
	*
	* @throws IOException
	* If an I/O error occurs, a communication error for example,
	* that cannot be identified as an error to indicate that the
	* operation failed in the target VM.
	*
	* @see java.lang.System#getProperties
	* @see #loadAgentLibrary
	* @see #loadAgent
	*/
	public abstract Properties getSystemProperties() throws IOException;

	/**
	* Returns the current <i>agent properties</i> in the target virtual
	* machine.
	*
	* <p> The target virtual machine can maintain a list of properties on
	* behalf of agents. The manner in which this is done, the names of the
	* properties, and the types of values that are allowed, is implementation
	* specific. Agent properties are typically used to store communication
	* end-points and other agent configuration details. For example, a debugger
	* agent might create an agent property for its transport address.
	*
	* <p> This method returns the agent properties whose key and value is a
	* <tt>String</tt>. Properties whose key or value is not a <tt>String</tt>
	* are omitted. If there are no agent properties maintained in the target
	* virtual machine then an empty property list is returned.
	*
	* @return The agent properties
	*
	* @throws AttachOperationFailedException
	* If the target virtual machine is unable to complete the
	* attach operation. A more specific error message will be
	* given by {@link AttachOperationFailedException#getMessage()}.
	*
	* @throws IOException
	* If an I/O error occurs, a communication error for example,
	* that cannot be identified as an error to indicate that the
	* operation failed in the target VM.
	*/
	public abstract Properties getAgentProperties() throws IOException;

	/**
	* Starts the JMX management agent in the target virtual machine.
	*
	* <p> The configuration properties are the same as those specified on
	* the command line when starting the JMX management agent. In the same
	* way as on the command line, you need to specify at least the
	* {@code com.sun.management.jmxremote.port} property.
	*
	* <p> See the online documentation for <a
	* href="../../../../../../../../technotes/guides/management/agent.html">
	* Monitoring and Management Using JMX Technology</a> for further details.
	*
	* @param agentProperties
	* A Properties object containing the configuration properties
	* for the agent.
	*
	* @throws AttachOperationFailedException
	* If the target virtual machine is unable to complete the
	* attach operation. A more specific error message will be
	* given by {@link AttachOperationFailedException#getMessage()}.
	*
	* @throws IOException
	* If an I/O error occurs, a communication error for example,
	* that cannot be identified as an error to indicate that the
	* operation failed in the target VM.
	*
	* @throws IllegalArgumentException
	* If keys or values in agentProperties are invalid.
	*
	* @throws NullPointerException
	* If agentProperties is null.
	*
	* @since 1.8
	*/
	public abstract void startManagementAgent(Properties agentProperties) throws IOException;

	/**
	* Starts the local JMX management agent in the target virtual machine.
	*
	* <p> See the online documentation for <a
	* href="../../../../../../../../technotes/guides/management/agent.html">
	* Monitoring and Management Using JMX Technology</a> for further details.
	*
	* @return The String representation of the local connector's service address.
	* The value can be parsed by the
	* {@link javax.management.remote.JMXServiceURL#JMXServiceURL(String)}
	* constructor.
	*
	* @throws AttachOperationFailedException
	* If the target virtual machine is unable to complete the
	* attach operation. A more specific error message will be
	* given by {@link AttachOperationFailedException#getMessage()}.
	*
	* @throws IOException
	* If an I/O error occurs, a communication error for example,
	* that cannot be identified as an error to indicate that the
	* operation failed in the target VM.
	*
	* @since 1.8
	*/
	public abstract String startLocalManagementAgent() throws IOException;

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

	/**
	* Tests this VirtualMachine for equality with another object.
	*
	* <p> If the given object is not a VirtualMachine then this
	* method returns <tt>false</tt>. For two VirtualMachines to
	* be considered equal requires that they both reference the same
	* provider, and their {@link VirtualMachineDescriptor#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 VirtualMachine that is equal to this
	* VirtualMachine.
	*/
	public boolean equals(Object ob) {
	if (ob == this)
	return true;
	if (!(ob instanceof VirtualMachine))
	return false;
	VirtualMachine other = (VirtualMachine)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>VirtualMachine</code>.
	*/
	public String toString() {
	return provider.toString() + ": " + id;
	}
	}

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