WeakReference.java

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package java.lang.ref;

/**
 * Weak reference objects, which do not prevent their referents from being
 * made finalizable, finalized, and then reclaimed.  Weak references are most
 * often used to implement canonicalizing mappings.
 *
 * <p> Suppose that the garbage collector determines at a certain point in time
 * that an object is <a href="package-summary.html#reachability">weakly
 * reachable</a>.  At that time it will atomically clear all weak references to
 * that object and all weak references to any other weakly-reachable objects
 * from which that object is reachable through a chain of strong and soft
 * references.  At the same time it will declare all of the formerly
 * weakly-reachable objects to be finalizable.  At the same time or at some
 * later time it will enqueue those newly-cleared weak references that are
 * registered with reference queues.
 *
 * @author Mark Reinhold
 * @since 1.2
 */
/*
 * 弱引用(Weak Reference)：
 * 当一个对象只剩弱引用时，运行GC后会回收其引用指向的对象。
 * 它可以用于解决非静态内部类的内存泄露问题（定义一个静态内部类，并让它持有外部类的弱引用）
 * 还可以用于实现缓存，比如WeakHashMap。
 */
public class WeakReference<T> extends Reference<T> {
    
    /**
     * Creates a new weak reference that refers to the given object.  The new
     * reference is not registered with any queue.
     *
     * @param referent object the new weak reference will refer to
     */
    public WeakReference(T referent) {
        super(referent);
    }
    
    /**
     * Creates a new weak reference that refers to the given object and is
     * registered with the given queue.
     *
     * @param referent object the new weak reference will refer to
     * @param q        the queue with which the reference is to be registered,
     *                 or {@code null} if registration is not required
     */
    public WeakReference(T referent, ReferenceQueue<? super T> q) {
        super(referent, q);
    }
    
}