System.gc和System.runFinalization区别
System.gc();
//告诉垃圾收集器打算进行垃圾收集，而垃圾收集器进不进行收集是不确定的
System.runFinalization();
//强制调用已经失去引用的对象的finalize方法
System.gc(); hints the VM that it is probably time to activate the Thread doing to the Garbage Collection. So all the part of this sentence stands in the hint word. The finalizer are run according to the VM good will, generally speaking. This means they could be run or could not. Invoking the System.runFinalization( ); force the VM to invoke on each instance the finalizer when it Garbage collects the Object referenced
