Java中的WeakHashMap浅析

//referent为引用指向的对象
 Reference(T referent) {
        this(referent, null);
    }
//ReferenceQueue对象，可以理解为队列
    Reference(T referent, ReferenceQueue<? super T> queue) {
        this.referent = referent;
        this.queue = (queue == null) ? ReferenceQueue.NULL : queue;
    }

Object o=new Object();
SoftReferencr sr=new SoftReference(o,queue);

public static void softReferenceDemo(){<!--{C}%3C!%2D%2D%20%2D%2D%3E--> Object o = new Object(); ReferenceQueue <Object> referenceQueue = new ReferenceQueue <Object>(); SoftReference <Object> softReference = new SoftReference <Object>(o, referenceQueue); System.out.println(softReference.get()); System.out.println(softReference.isEnqueued()); System.out.println(referenceQueue.poll()); /** * java.lang.Object@4aa594e1 * false * null */ /** * 当对象被回收时，他会放入到referenceQueue实例中 */ //创建比较大的对象，模拟内存不足，触发GC，回收软引用对象 byte[] bytes = new byte[7*1024*1024]; System.gc(); //手动触发GC /** * 理论上空间不足,对象会被回收，队列中会有软引用对象 */ System.out.println(softReference.get()); System.out.println(softReference.isEnqueued()); System.out.println(referenceQueue.poll()); /** * java.lang.Object@4aa594e1 false null 空间充足，未回收 */ } public static void softReferenceDemo(){
        Object o = new Object();
        ReferenceQueue <Object> referenceQueue = new ReferenceQueue <Object>();
        SoftReference <Object> softReference = new SoftReference <Object>(o, referenceQueue);
        System.out.println(softReference.get());
        System.out.println(softReference.isEnqueued());
        System.out.println(referenceQueue.poll());
        /**
         * java.lang.Object@4aa594e1
         * false
         * null
         */
        /**
         * 当对象被回收时，他会放入到referenceQueue实例中
         */
        //创建比较大的对象，模拟内存不足，触发GC，回收软引用对象
        byte[] bytes = new byte[7*1024*1024];
        System.gc(); //手动触发GC
        /**
         * 理论上空间不足,对象会被回收，队列中会有软引用对象
         */
        System.out.println(softReference.get());
        System.out.println(softReference.isEnqueued());
        System.out.println(referenceQueue.poll());
        /**
         *
         java.lang.Object@4aa594e1
         false
         null
         空间充足，未回收
         */
    }

 public static void weakReferenceDemo(){
        Object o = new Object();
        ReferenceQueue <Object> referenceQueue = new ReferenceQueue <Object>();
        WeakReference <Object> weakReference = new WeakReference<Object>(o, referenceQueue);
        System.out.println(weakReference.get());
        System.out.println(weakReference.isEnqueued());
        System.out.println(referenceQueue.poll());
        System.gc(); //手动触发GC
        System.out.println(weakReference.get());
        System.out.println(weakReference.isEnqueued());
        System.out.println(referenceQueue.poll());
    }

public static void phantomferenceDemo(){
        Object o = new Object();
        ReferenceQueue <Object> referenceQueue = new ReferenceQueue <Object>();
        PhantomReference <Object> phantomReference = new PhantomReference<Object>(o, referenceQueue);
        o = null;
        System.gc(); //手动触发GC
        if (phantomReference.isEnqueued()) {
            System.out.println("正在被回收");
        } else {
            System.out.println("没有被回收");
        }
    }