finalize机制

概述

public class Object {
 
    protected void finalize() throws Throwable { }
 
}

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
A subclass overrides the {@code finalize} method to dispose of system resources or to perform other cleanup.

当GC确定对该对象没有引用，由GC调用；

子类可以重写finalize方法 来处理系统资源或执行其他清理；

The {@code finalize} method may take any action, including making this object available again to other threads; the usual purpose of {@code finalize}, however, is to perform cleanup actions before the object is irrevocably discarded.
For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.

finalize方法可以执行任何操作，包括使对象再次被可用；但是通常用途在对象被丢弃前执行清理（中断连接...）；

The {@code finalize} method is never invoked more than once by a Java virtual machine for any given object.

finalize方法仅被GC调用一次；

示例

public static void main(String[] args) throws InterruptedException {
 
        WeakReference<MyFinalize> weakReference = new WeakReference<>(new MyFinalize());   //弱引用，只要GC就会被回收
 
        System.gc();
 
        Thread.sleep(10000);
 
        if (null == weakReference.get()){
            System.out.println("myFinalize is dead");
        }
        else {
            System.out.println("myFinalize is still alive");
        }
    }
 
    static class MyFinalize{
 
        @Override
        protected void finalize() throws Throwable {
            System.out.println("gc call finalize...");
        }
    }
 
结果：
gc call finalize...
myFinalize is dead

public static void main(String[] args) throws InterruptedException {
 
        MyFinalize myFinalize = new MyFinalize();
 
        myFinalize = null;  //移除对象的强引用
 
        System.gc();
 
        Thread.sleep(10000);
 
        if (null == myFinalize){
            System.out.println("myFinalize is dead");
        }
        else {
            System.out.println("myFinalize is still alive");
        }
    }
 
    static class MyFinalize{
 
        @Override
        protected void finalize() throws Throwable {
            System.out.println("gc call finalize...");
        }
    }
 
 
结果：
gc call finalize...
myFinalize is dead