1、使用说明还是从测试例子开始说明，首先添加一个TestWeakReference测试例子/*** 测试弱引用* Created by shaowei on 2017/8/14.*/public class TestWeakReferece { public static void main(String[] args) { Object o = new Object(); WeakReference<Object> weak = new WeakReference<Object>(o); o = null; int i = 0; while (weak.get() != null) { i++; System.out.println("Object is not null. count is " + i); if (i % 10 == 0) { System.gc(); System.out.println("System.gc() was called!"); } try { Thread.sleep(500); } catch (InterruptedException e) { } } System.out.println("object o was cleared by JVM!"); }}
3、从示例代码中可以看出，WeakReference对象一直持有o对象，就是因为WeakReference类是弱引用持有o对象，才没有影响到垃圾回收器对o对象的回收。我们后续使用WeakReference时，就如图本例测试代码一样去构造WeakReference对象然后持有我们需要弱引用控制的类
5、ThreadLocalMap类构造器里创建了Entry集合来存放以ThreadLocal为key的一个value值
7、这个地方用到弱引用，即ThreadLocal对象回收不会被这里的Entry所影响
