垃圾回收的可触及性

/**
 * Created by xxd on 2017/4/4.
 */
public class CanReliveObj {
    public static CanReliveObj obj;

    @Override
    protected  void finalize() throws Throwable{
        super.finalize();
        System.out.println("CanReliveObj finalize called");
        obj = this;
    }

    @Override
    public String toString(){
        return "I am CanReliveObj";
    }

    public static void main(String[] args) throws InterruptedException{
        obj = new CanReliveObj();
        obj = null;
        System.gc();
        Thread.sleep(1000);
        if (obj == null){
            System.out.println("obj is null");
        }else{
            System.out.println("obj is useful");
        }
        System.out.println("the second gc");
        obj = null;
        System.gc();
        Thread.sleep(1000);
        if (obj == null){
            System.out.println("obj is null");
        }else{
            System.out.println("obj is useful");
        }
    }
}