| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package java.lang.ref; |
| |
| /** |
| * Provides an abstract class which describes behavior common to all reference |
| * objects. It is not possible to create immediate subclasses of |
| * {@code Reference} in addition to the ones provided by this package. It is |
| * also not desirable to do so, since references require very close cooperation |
| * with the system's garbage collector. The existing, specialized reference |
| * classes should be used instead. |
| * |
| * @since 1.2 |
| */ |
| public abstract class Reference<T> { |
| |
| /* |
| * This class must be implemented by the vm vendor. The documented methods must |
| * be implemented to support the provided subclass implementations. As the |
| * provided subclass implementations are trivial and simply call |
| * initReference(Object) and initReference(Object, ReferenceQueue) from their |
| * constructors, the vm vendor may elect to implement the subclasses as well. |
| * Abstract class which describes behavior common to all reference objects. |
| */ |
| |
| /** |
| * Constructs a new instance of this class. |
| * |
| */ |
| Reference() { |
| super(); |
| } |
| |
| /** |
| * Makes the referent {@code null}. This does not force the reference |
| * object to be enqueued. |
| */ |
| public void clear() { |
| return; |
| } |
| |
| /** |
| * Forces the reference object to be enqueued if it has been associated with |
| * a queue. |
| * |
| * @return {@code true} if this call has caused the {@code Reference} to |
| * become enqueued, or {@code false} otherwise |
| */ |
| public boolean enqueue() { |
| return false; |
| } |
| |
| /** |
| * Returns the referent of the reference object. |
| * |
| * @return the referent to which reference refers, or {@code null} if the |
| * object has been cleared. |
| */ |
| public T get() { |
| return null; |
| } |
| |
| /** |
| * Checks whether the reference object has been enqueued. |
| * |
| * @return {@code true} if the {@code Reference} has been enqueued, {@code |
| * false} otherwise |
| */ |
| public boolean isEnqueued() { |
| return false; |
| } |
| |
| /** |
| * Implement this method to support the provided subclass implementations. |
| * Initialize a newly created reference object. Associate the reference |
| * object with the referent. |
| * |
| * @param r the referent |
| */ |
| void initReference(Object r) { |
| return; |
| } |
| |
| /** |
| * Implement this method to support the provided subclass implementations. |
| * Initialize a newly created reference object. Associate the reference |
| * object with the referent, and the specified ReferenceQueue. |
| * |
| * @param r the referent |
| * @param q the ReferenceQueue |
| */ |
| void initReference(Object r, ReferenceQueue<? super T> q) { |
| return; |
| } |
| |
| /** |
| * Enqueue the reference object on the associated queue. |
| * |
| * @return boolean true if the Reference was successfully enqueued. false |
| * otherwise. |
| */ |
| boolean enqueueImpl() { |
| return false; |
| } |
| |
| /** |
| * Called when a Reference has been removed from its ReferenceQueue. Set the |
| * enqueued field to false. |
| */ |
| void dequeue() { |
| return; |
| } |
| } |