WeakHashMap的remove方法导致对象回收的测试

    定义一个类，在finalize方法中添加log public class Test{         int value;
        public Test() {             // TODO Auto-generated constructor stub         }
        public Test(int i) {             // TODO Auto-generated constructor stub             value = i;         }
        @Override         protected void finalize() throws Throwable {             // TODO Auto-generated method stub             System.out.println("Test finalize,value=" + value                      + ", this=" + this);
            super.finalize();         }     }
    public void testWMap()     {         //test WeakHashMap         WeakHashMapwmap = new WeakHashMap();         wmap.put(""+1, new Test(1));         wmap.put(""+2, new Test(2));         wmap.put(""+3, new Test(3));         wmap.put(""+4, new Test(4));         wmap.put(""+5, new Test(5));
        System.gc();         System.out.println("wmap.size=" + wmap.size());         wmap.remove("1");
        System.out.println("wmap.size=" + wmap.size());
        for (int i = 6; i < 30; i++) {             wmap.put(""+i, new Test(i));
            System.out.println("== wmap.size=" + wmap.size());         }         //gc do not make the Test object to release         //but remove from the weakmap and than gc can make it release         System.gc();         wmap.remove("2");         for (int i = 0; i < wmap.size(); i++) {
            System.out.println("key=" + wmap.keySet().toArray()[i]);         }         System.out.println("== wmap.size=" + wmap.size()); //        System.gc();
    }
调用testWMap()
wmap.size=5wmap.size=4== wmap.size=5== wmap.size=6== wmap.size=7== wmap.size=8== wmap.size=9== wmap.size=10== wmap.size=11== wmap.size=12== wmap.size=13== wmap.size=14== wmap.size=15== wmap.size=16== wmap.size=17== wmap.size=18== wmap.size=19== wmap.size=20== wmap.size=21== wmap.size=22== wmap.size=23== wmap.size=24== wmap.size=25== wmap.size=26== wmap.size=27== wmap.size=28Test finalize,value=1, this=com.foxx.a.File1$Test@ca0b6key=4key=5key=3== wmap.size=3
可以看出，WeakHashMap中没有被引用的对象可能会被WeakHashMap去掉（remove） 被remove后，再System.gc()，才能够让对象及时的被回收。 WeakHashMap自动remove难以确定何时进行，必要的时候，还是需要调用remove方法

修改为     public void testWMap()    {        //test WeakHashMap        WeakHashMapwmap = new WeakHashMap();        wmap.put(""+1, new Test(1));        wmap.put(""+2, new Test(2));        wmap.put(""+3, new Test(3));        wmap.put(""+4, new Test(4));        wmap.put(""+5, new Test(5));
        System.gc();        System.out.println("wmap.size=" + wmap.size());        wmap.remove("1");
        System.out.println("wmap.size=" + wmap.size());
        for (int i = 6; i < 30; i++) {            wmap.put(""+i, new Test(i));
            System.out.println("== wmap.size=" + wmap.size());        }        //gc do not make the Test object to release        //but remove from the weakmap and than gc can make it release        System.gc();        wmap.remove("2");        for (int i = 0; i < wmap.size(); i++) {
            System.out.println("key=" + wmap.keySet().toArray()[i]);        }        System.out.println("== wmap.size=" + wmap.size());        System.gc();
    }
对象都会被回收 wmap.size=5wmap.size=4== wmap.size=5== wmap.size=6== wmap.size=7== wmap.size=8== wmap.size=9== wmap.size=10== wmap.size=11== wmap.size=12== wmap.size=13== wmap.size=14== wmap.size=15== wmap.size=16== wmap.size=17== wmap.size=18== wmap.size=19== wmap.size=20== wmap.size=21== wmap.size=22== wmap.size=23== wmap.size=24== wmap.size=25== wmap.size=26== wmap.size=27== wmap.size=28Test finalize,value=1, this=com.foxx.a.File1$Test@1a758cbkey=4key=5key=3== wmap.size=3Test finalize,value=13, this=com.foxx.a.File1$Test@69b332Test finalize,value=29, this=com.foxx.a.File1$Test@173a10fnewString=com.UCMobileTest finalize,value=28, this=com.foxx.a.File1$Test@530daaTest finalize,value=27, this=com.foxx.a.File1$Test@a62fc3
Test finalize,value=26, this=com.foxx.a.File1$Test@89ae9e
Test finalize,value=25, this=com.foxx.a.File1$Test@1270b73 Test finalize,value=24, this=com.foxx.a.File1$Test@60aeb0
Test finalize,value=23, this=com.foxx.a.File1$Test@16caf43

Test finalize,value=22, this=com.foxx.a.File1$Test@66848cTest finalize,value=21, this=com.foxx.a.File1$Test@8813f2Test finalize,value=20, this=com.foxx.a.File1$Test@1d58aaeTest finalize,value=19, this=com.foxx.a.File1$Test@83cc67Test finalize,value=18, this=com.foxx.a.File1$Test@e09713Test finalize,value=17, this=com.foxx.a.File1$Test@156ee8eTest finalize,value=16, this=com.foxx.a.File1$Test@47b480Test finalize,value=15, this=com.foxx.a.File1$Test@10d448
Test finalize,value=14, this=com.foxx.a.File1$Test@e0e1c6
Test finalize,value=12, this=com.foxx.a.File1$Test@6ca1cTest finalize,value=11, this=com.foxx.a.File1$Test@1bf216aTest finalize,value=10, this=com.foxx.a.File1$Test@12ac982Test finalize,value=9, this=com.foxx.a.File1$Test@1389e4Test finalize,value=8, this=com.foxx.a.File1$Test@c20e24Test finalize,value=7, this=com.foxx.a.File1$Test@2e7263Test finalize,value=6, this=com.foxx.a.File1$Test@157f0dcTest finalize,value=2, this=com.foxx.a.File1$Test@863399