/* * Copyright (c) 1998, 2006, 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.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 */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.     * The method, in this case, must not belong to an interface and     * must not be abstract. This option is useful for performing method     * invocations like those done with the <code>super</code> keyword in     * the Java programming language.     * <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     * does not match the number of declared arguemnts for the method,     * if the method is a constructor or static intializer, or     * if {@link #INVOKE_NONVIRTUAL} is specified and the method is     * either abstract or an interface member.     * @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();}