对象的finalize调用链和clone调用链一样，必须手工构造

class A {  
      
    public A() {  
        System.out.println("A construct");    
    }  
  
    @Override  
    public void finalize() {  
        System.out.println("A finalize");    
    }  
}  
  
class B extends A{  
    String name;  
    int age;  
  
    public B(String name, int age) {  
        this.name = name;  
        this.age = age;  
		System.out.println("B construct "+name+" is "+age);    
    }  
  
    @Override  
    public void finalize() {  
        System.out.println("B finalize"); 
		super.finalize();
    }  
  

}  
  
public class Main {  
    public static void main(String[] args) throws Exception {  
        A a = new B("allen", 20);  
		a=null;
		System.gc();
    }  
}  
/*A construct
B construct allen is 20
B finalize
A finalize*/