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

        WeakHashMap<String, Test>wmap = new WeakHashMap<String, Test>();

        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=5

wmap.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=28

Test finalize,value=1, this=com.foxx.a.File1$Test@ca0b6

key=4

key=5

key=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

        WeakHashMap<String, Test>wmap = new WeakHashMap<String, Test>();

        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=5

wmap.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=28

Test finalize,value=1, this=com.foxx.a.File1$Test@1a758cb

key=4

key=5

key=3

== wmap.size=3

Test finalize,value=13, this=com.foxx.a.File1$Test@69b332

Test finalize,value=29, this=com.foxx.a.File1$Test@173a10f

newString=com.UCMobile

Test finalize,value=28, this=com.foxx.a.File1$Test@530daa

Test 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@66848c

Test finalize,value=21, this=com.foxx.a.File1$Test@8813f2

Test finalize,value=20, this=com.foxx.a.File1$Test@1d58aae

Test finalize,value=19, this=com.foxx.a.File1$Test@83cc67

Test finalize,value=18, this=com.foxx.a.File1$Test@e09713

Test finalize,value=17, this=com.foxx.a.File1$Test@156ee8e

Test finalize,value=16, this=com.foxx.a.File1$Test@47b480

Test 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@6ca1c

Test finalize,value=11, this=com.foxx.a.File1$Test@1bf216a

Test finalize,value=10, this=com.foxx.a.File1$Test@12ac982

Test finalize,value=9, this=com.foxx.a.File1$Test@1389e4

Test finalize,value=8, this=com.foxx.a.File1$Test@c20e24

Test finalize,value=7, this=com.foxx.a.File1$Test@2e7263

Test finalize,value=6, this=com.foxx.a.File1$Test@157f0dc

Test finalize,value=2, this=com.foxx.a.File1$Test@863399