Reference Soft Strong Weak

今天被问及了应用的区别，具体如下

参考一下understanding-weak-reference

 

four different degrees of reference strength: strong, soft, weak, and phantom, in order from strongest to weakest.

 

Strong Reference 主要是只通过 Object obj = new Object()这种方式产生的应用.

Strong Reference 只有在obj == null 的情况下， 对象才会在GC的时候被回收。

 

SoftReference 的目的是在当应用为0的情况下，仍然不会回收该对象，知道JVM内存不够用的时候就会被回收。

an object which is softly reachable will generally stick around for a while.

 

WeakReference

String因为是放入常量池因此

WeakHashMap<Object , String> weakMap = new WeakHashMap<Object, String>(); //如果这里用String作为Key的话,就无法起到WeakReference的效果 Object key1 = new Object(); weakMap.put(key1, new Object().toString()); System.out.println(weakMap); key1 = null; System.gc(); //Thread.sleep(5000); System.out.println(weakMap);