测试WeakReference和PhantomReference

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介绍强引用(strong reference)、软引用(soft reference)、弱引用(weak reference)和虚引用(phantom reference)

下面测试WeakReference和PhantomReference

import java.lang.ref.PhantomReference;import java.lang.ref.Reference;import java.lang.ref.ReferenceQueue;import java.lang.ref.WeakReference;public class ReferenceTest {@SuppressWarnings("unchecked")public static void main(String[] args) {Reference<Object> ref;Object weakObj = new String("weak reference");Object phantomObj = new String("phantom reference");ReferenceQueue<Object> weakQueue = new ReferenceQueue<Object>();ReferenceQueue<Object> phantomQueue = new ReferenceQueue<Object>();WeakReference<Object> weakReference = new WeakReference<Object>(weakObj, weakQueue);PhantomReference<Object> phantomReference = new PhantomReference<Object>(phantomObj, phantomQueue);weakObj = null;phantomObj = null;System.out.println("Weak Reference: "+weakReference.get());System.out.println("Phantom Reference: "+phantomReference.get());//nullSystem.gc();//弱引用、虚引用被回收，同时加入到相关ReferenceQueueSystem.out.println("Weak Reference: "+weakReference.get());//nullSystem.out.println("Phantom Reference: "+phantomReference.get());//nullif(!phantomReference.isEnqueued()) {System.out.println("Request finalization.");System.runFinalization();}System.out.println("weak is queued: "+weakReference.isEnqueued());//trueSystem.out.println("Phantom Queued: " + phantomReference.isEnqueued());//truetry {  ref = (Reference<Object>) weakQueue.remove();  System.out.println("Weak Reference: " + ref.get());//nullref = (Reference<Object>) phantomQueue.remove();  System.out.println("Phantom Reference: " + ref.get());//nullref.clear();  } catch(InterruptedException e) {  e.printStackTrace();  } }}

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