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import java.lang.ref.*;

/**

* Description:

* <br/>网站: <a href="http://www.crazyit.org">疯狂Java联盟</a>

* <br/>Copyright (C), 2001-2016, Yeeku.H.Lee

* <br/>This program is protected by copyright laws.

* <br/>Program Name:

* <br/>Date:

* @author Yeeku.H.Lee kongyeeku@163.com

* @version 1.0

*/

public class PhantomReferenceTest

{

public static void main(String[] args)

throws Exception

{

// 创建一个字符串对象

String str = new String("疯狂Java讲义");

// 创建一个引用队列

ReferenceQueue rq = new ReferenceQueue();

// 创建一个虚引用，让此虚引用引用到"疯狂Java讲义"字符串

PhantomReference pr = new PhantomReference (str , rq);

// 切断str引用和"疯狂Java讲义"字符串之间的引用

str = null;

// 取出虚引用所引用的对象，并不能通过虚引用获取被引用的对象，所以此处输出null

System.out.println(pr.get()); //①

// 强制垃圾回收

System.gc();

System.runFinalization();

// 垃圾回收之后，虚引用将被放入引用队列中

// 取出引用队列中最先进入队列中的引用与pr进行比较

System.out.println(rq.poll() == pr); //②

}

}