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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * 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,

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package com.sun.jdi;

import java.util.List;

import java.util.Map;

/**

 * An object that currently exists in the target VM. An ObjectReference

 * mirrors only the object itself and is not specific to any

 * {@link Field} or {@link LocalVariable} to which it is currently

 * assigned. An ObjectReference can

 * have 0 or more references from field(s) and/or variable(s).

 * <p>

 * Any method on <code>ObjectReference</code> which directly or

 * indirectly takes <code>ObjectReference</code> as an parameter may throw

 * {@link com.sun.jdi.VMDisconnectedException} if the target VM is

 * disconnected and the {@link com.sun.jdi.event.VMDisconnectEvent} has been or is

 * available to be read from the {@link com.sun.jdi.event.EventQueue}.

 * <p>

 * Any method on <code>ObjectReference</code> which directly or

 * indirectly takes <code>ObjectReference</code> as an parameter may throw

 * {@link com.sun.jdi.VMOutOfMemoryException} if the target VM has run out of memory.

 * <p>

 * Any method on <code>ObjectReference</code> or which directly or indirectly takes

 * <code>ObjectReference</code> as parameter may throw

 * {@link com.sun.jdi.ObjectCollectedException} if the mirrored object has been

 * garbage collected.

 *

 * @author Robert Field

 * @author Gordon Hirsch

 * @author James McIlree

 * @since  1.3

 */

@jdk.Exported

public interface ObjectReference extends Value {

    /**

     * Gets the {@link ReferenceType} that mirrors the type

     * of this object. The type may be a subclass or implementor of the

     * declared type of any field or variable which currently holds it.

     * For example, right after the following statement.

     * <p>

     * <code>Object obj = new String("Hello, world!");</code>

     * <p>

     * The ReferenceType of obj will mirror java.lang.String and not

     * java.lang.Object.

     * <p>

     * The type of an object never changes, so this method will

     * always return the same ReferenceType over the lifetime of the

     * mirrored object.

     * <p>

     * The returned ReferenceType will be a {@link ClassType} or

     * {@link ArrayType} and never an {@link InterfaceType}.

     *

     * @return the {@link ReferenceType} for this object.

     */

    ReferenceType referenceType();

    /**

     * Gets the value of a given instance or static field in this object.

     * The Field must be valid for this ObjectReference;

     * that is, it must be from

     * the mirrored object's class or a superclass of that class.

     *

     * @param sig the field containing the requested value

     * @return the {@link Value} of the instance field.

     * @throws java.lang.IllegalArgumentException if the field is not valid for

     * this object's class.

     */

    Value getValue(Field sig);

    /**

     * Gets the value of multiple instance and/or static fields in this object.

     * The Fields must be valid for this ObjectReference;

     * that is, they must be from

     * the mirrored object's class or a superclass of that class.

     *

     * @param fields a list of {@link Field} objects containing the

     * requested values.

     * @return a Map of the requested {@link Field} objects with

     * their {@link Value}.

     * @throws java.lang.IllegalArgumentException if any field is not valid for

     * this object's class.

     */

    Map<Field,Value> getValues(List<? extends Field> fields);

    /**

     * Sets the value of a given instance or static field in this object.

     * The {@link Field} must be valid for this ObjectReference; that is,

     * it must be from the mirrored object's class or a superclass of that class.

     * If static, the field must not be final.

     * <p>

     * Object values must be assignment compatible with the field type

     * (This implies that the field type must be loaded through the

     * enclosing class's class loader). Primitive values must be

     * either assignment compatible with the field type or must be

     * convertible to the field type without loss of information.

     * See section 5.2 of

     * <cite>The Java&trade; Language Specification</cite>

     * for more information on assignment

     * compatibility.

     *

     * @param field the field containing the requested value

     * @param value the new value to assign

     * @throws java.lang.IllegalArgumentException if the field is not valid for

     * this object's class.

     * @throws InvalidTypeException if the value's type does not match

     * the field's type.

     * @throws ClassNotLoadedException if 'value' is not null, and the field

     * type has not yet been loaded through the appropriate class loader.

     * @throws VMCannotBeModifiedException if the VirtualMachine is read-only - see {@link VirtualMachine#canBeModified()}.

     */

    void setValue(Field field, Value value)

        throws InvalidTypeException, ClassNotLoadedException;

    /** Perform method invocation with only the invoking thread resumed */

    static final int INVOKE_SINGLE_THREADED = 0x1;

    /** Perform non-virtual method invocation */

    static final int INVOKE_NONVIRTUAL      = 0x2;

    /**

     * Invokes the specified {@link Method} on this object in the

     * target VM. The

     * specified method can be defined in this object's class,

     * in a superclass of this object's class, or in an interface

     * implemented by this object. The method may be a static method

     * or an instance method, but not a static initializer or constructor.

     * Use {@link ClassType#newInstance} to create a new object and

     * run its constructor.

     * <p>

     * The method invocation will occur in the specified thread.

     * Method invocation can occur only if the specified thread

     * has been suspended by an event which occurred in that thread.

     * Method invocation is not supported

     * when the target VM has been suspended through

     * {@link VirtualMachine#suspend} or when the specified thread

     * is suspended through {@link ThreadReference#suspend}.

     * <p>

     * The specified method is invoked with the arguments in the specified

     * argument list.  The method invocation is synchronous; this method

     * does not return until the invoked method returns in the target VM.

     * If the invoked method throws an exception, this method

     * will throw an {@link InvocationException} which contains

     * a mirror to the exception object thrown.

     * <p>

     * Object arguments must be assignment compatible with the argument type

     * (This implies that the argument type must be loaded through the

     * enclosing class's class loader). Primitive arguments must be

     * either assignment compatible with the argument type or must be

     * convertible to the argument type without loss of information.

     * If the method being called accepts a variable number of arguments,

     * then the last argument type is an array of some component type.

     * The argument in the matching position can be omitted, or can be null,

     * an array of the same component type, or an argument of the

     * component type followed by any number of other arguments of the same

     * type. If the argument is omitted, then a 0 length array of the

     * component type is passed.  The component type can be a primitive type.

     * Autoboxing is not supported.

     *

     * See section 5.2 of

     * <cite>The Java&trade; Language Specification</cite>

     * for more information on assignment compatibility.

     * <p>

     * By default, the method is invoked using dynamic lookup as

     * documented in section 15.12.4.4 of

     * <cite>The Java&trade; Language Specification</cite>

     * in particular, overriding based on the runtime type of the object

     * mirrored by this {@link ObjectReference} will occur. This

     * behavior can be changed by specifying the

     * {@link #INVOKE_NONVIRTUAL} bit flag in the <code>options</code>

     * argument. If this flag is set, the specified method is invoked

     * whether or not it is overridden for this object's runtime type.

     * <p>

     * By default, all threads in the target VM are resumed while

     * the method is being invoked if they were previously

     * suspended by an event or by {@link VirtualMachine#suspend} or

     * {@link ThreadReference#suspend}. This is done to prevent the deadlocks

     * that will occur if any of the threads own monitors

     * that will be needed by the invoked method.

     * Note, however, that this implicit resume acts exactly like

     * {@link ThreadReference#resume}, so if the thread's suspend

     * count is greater than 1, it will remain in a suspended state

     * during the invocation and thus a deadlock could still occur.

     * By default, when the invocation completes,

     * all threads in the target VM are suspended, regardless their state

     * before the invocation.

     * It is possible that

     * breakpoints or other events might occur during the invocation.

     * This can cause deadlocks as described above. It can also cause a deadlock

     * if invokeMethod is called from the client's event handler thread.  In this

     * case, this thread will be waiting for the invokeMethod to complete and

     * won't read the EventSet that comes in for the new event.  If this

     * new EventSet is SUSPEND_ALL, then a deadlock will occur because no

     * one will resume the EventSet.  To avoid this, all EventRequests should

     * be disabled before doing the invokeMethod, or the invokeMethod should

     * not be done from the client's event handler thread.

     * <p>

     * The resumption of other threads during the invocation can be prevented

     * by specifying the {@link #INVOKE_SINGLE_THREADED}

     * bit flag in the <code>options</code> argument; however,

     * there is no protection against or recovery from the deadlocks

     * described above, so this option should be used with great caution.

     * Only the specified thread will be resumed (as described for all

     * threads above). Upon completion of a single threaded invoke, the invoking thread

     * will be suspended once again. Note that any threads started during

     * the single threaded invocation will not be suspended when the

     * invocation completes.

     * <p>

     * If the target VM is disconnected during the invoke (for example, through

     * {@link VirtualMachine#dispose}) the method invocation continues.

     *

     * @param thread the thread in which to invoke.

     * @param method the {@link Method} to invoke.

     * @param arguments the list of {@link Value} arguments bound to the

     * invoked method. Values from the list are assigned to arguments

     * in the order they appear in the method signature.

     * @param options the integer bit flag options.

     * @return a {@link Value} mirror of the invoked method's return value.

     * @throws java.lang.IllegalArgumentException if the method is not

     * a member of this object's class, if the size of the argument list

     * if the method is a constructor or static intializer, or

     * if {@link #INVOKE_NONVIRTUAL} is specified and the method is

     * @throws {@link InvalidTypeException} if any argument in the

     * argument list is not assignable to the corresponding method argument

     * type.

     * @throws ClassNotLoadedException if any argument type has not yet been loaded

     * through the appropriate class loader.

     * @throws IncompatibleThreadStateException if the specified thread has not

     * been suspended by an event.

     * @throws InvocationException if the method invocation resulted in

     * an exception in the target VM.

     * @throws InvalidTypeException If the arguments do not meet this requirement --

     *         Object arguments must be assignment compatible with the argument

     *         type.  This implies that the argument type must be

     *         loaded through the enclosing class's class loader.

     *         Primitive arguments must be either assignment compatible with the

     *         argument type or must be convertible to the argument type without loss

     *         of information. See JLS section 5.2 for more information on assignment

     *         compatibility.

     * @throws VMCannotBeModifiedException if the VirtualMachine is read-only - see {@link VirtualMachine#canBeModified()}.

     */

    Value invokeMethod(ThreadReference thread, Method method,

                       List<? extends Value> arguments, int options)

                                   throws InvalidTypeException,

                                          ClassNotLoadedException,

                                          IncompatibleThreadStateException,

                                          InvocationException;

    /**

     * Prevents garbage collection for this object. By default all

     * {@link ObjectReference} values returned by JDI may be collected

     * at any time the target VM is running. A call to this method

     * guarantees that the object will not be collected.

     * {@link #enableCollection} can be used to allow collection once

     * again.

     * <p>

     * Calls to this method are counted. Every call to this method

     * requires a corresponding call to {@link #enableCollection} before

     * garbage collection is re-enabled.

     * <p>

     * Note that while the target VM is suspended, no garbage collection

     * will occur because all threads are suspended. The typical

     * examination of variables, fields, and arrays during the suspension

     * is safe without explicitly disabling garbage collection.

     * <p>

     * This method should be used sparingly, as it alters the

     * pattern of garbage collection in the target VM and,

     * consequently, may result in application behavior under the

     * debugger that differs from its non-debugged behavior.

     * @throws VMCannotBeModifiedException if the VirtualMachine is read-only

     * -see {@link VirtualMachine#canBeModified()}.

     */

    void disableCollection();

    /**

     * Permits garbage collection for this object. By default all

     * {@link ObjectReference} values returned by JDI may be collected

     * at any time the target VM is running. A call to this method

     * is necessary only if garbage collection was previously disabled

     * with {@link #disableCollection}.

     * @throws VMCannotBeModifiedException if the VirtualMachine is read-only

     * -see {@link VirtualMachine#canBeModified()}.

     */

    void enableCollection();

    /**

     * Determines if this object has been garbage collected in the target

     * VM.

     *

     * @return <code>true</code> if this {@link ObjectReference} has been collected;

     * <code>false</code> otherwise.

     * @throws VMCannotBeModifiedException if the VirtualMachine is read-only

     * -see {@link VirtualMachine#canBeModified()}.

     */

    boolean isCollected();

    /**

     * Returns a unique identifier for this ObjectReference.

     * It is guaranteed to be unique among all

     * ObjectReferences from the same VM that have not yet been disposed.

     * The guarantee applies as long

     * as this ObjectReference has not yet been disposed.

     *

     * @return a long unique ID

     */

    long uniqueID();

    /**

     * Returns a List containing a {@link ThreadReference} for

     * each thread currently waiting for this object's monitor.

     * See {@link ThreadReference#currentContendedMonitor} for

     * information about when a thread is considered to be waiting

     * for a monitor.

     * <p>

     * Not all target VMs support this operation. See

     * VirtualMachine#canGetMonitorInfo to determine if the

     * operation is supported.

     *

     * @return a List of {@link ThreadReference} objects. The list

     * has zero length if no threads are waiting for the monitor.

     * @throws java.lang.UnsupportedOperationException if the

     * target VM does not support this operation.

     * @throws IncompatibleThreadStateException if any

     * waiting thread is not suspended

     * in the target VM

     */

    List<ThreadReference> waitingThreads()

        throws IncompatibleThreadStateException;

    /**

     * Returns an {@link ThreadReference} for the thread, if any,

     * which currently owns this object's monitor.

     * See {@link ThreadReference#ownedMonitors} for a definition

     * of ownership.

     * <p>

     * Not all target VMs support this operation. See

     * VirtualMachine#canGetMonitorInfo to determine if the

     * operation is supported.

     *

     * @return the {@link ThreadReference} which currently owns the

     * monitor, or null if it is unowned.

     *

     * @throws java.lang.UnsupportedOperationException if the

     * target VM does not support this operation.

     * @throws IncompatibleThreadStateException if the owning thread is

     * not suspended in the target VM

     */

    ThreadReference owningThread() throws IncompatibleThreadStateException;

    /**

     * Returns the number times this object's monitor has been

     * entered by the current owning thread.

     * See {@link ThreadReference#ownedMonitors} for a definition

     * of ownership.

     * <p>

     * Not all target VMs support this operation. See

     * VirtualMachine#canGetMonitorInfo to determine if the

     * operation is supported.

     *

     * @see #owningThread

     * @return the integer count of the number of entries.

     *

     * @throws java.lang.UnsupportedOperationException if the

     * target VM does not support this operation.

     * @throws IncompatibleThreadStateException if the owning thread is

     * not suspended in the target VM

     */

    int entryCount() throws IncompatibleThreadStateException;

    /**

     * Returns objects that directly reference this object.

     * Only objects that are reachable for the purposes of garbage collection

     * are returned.  Note that an object can also be referenced in other ways,

     * such as from a local variable in a stack frame, or from a JNI global

     * reference.  Such non-object referrers are not returned by this method.

     * <p>

     * Not all target virtual machines support this operation.

     * Use {@link VirtualMachine#canGetInstanceInfo()}

     * to determine if the operation is supported.

     *

     * @see VirtualMachine#instanceCounts(List)

     * @see ReferenceType#instances(long)

     * @param maxReferrers  The maximum number of referring objects to return.

     *                      Must be non-negative.  If zero, all referring

     *                      objects are returned.

     * @return a of List of {@link ObjectReference} objects. If there are

     *  no objects that reference this object, a zero-length list is returned..

     * @throws java.lang.UnsupportedOperationException if

     * the target virtual machine does not support this

     * operation - see

     * {@link VirtualMachine#canGetInstanceInfo() canGetInstanceInfo()}

     * @throws java.lang.IllegalArgumentException if maxReferrers is less

     *         than zero.

     * @since 1.6

     */

    List<ObjectReference> referringObjects(long maxReferrers);

    /**

     * Compares the specified Object with this ObjectReference for equality.

     *

     * @return  true if the Object is an ObjectReference, if the

     * ObjectReferences belong to the same VM, and if applying the

     * "==" operator on the mirrored objects in that VM evaluates to true.

     */

    boolean equals(Object obj);

    /**

     * Returns the hash code value for this ObjectReference.

     *

     * @return the integer hash code

     */

    int hashCode();

}