【java】对象克隆protected Object clone() throws CloneNotSupportedException

package 对象克隆;
class A implements Cloneable{//要具备clone()功能必须要实现Cloneable接口，此接口里无方法，只起标识作用。
    private String value;
    public A(String value){
        this.value=value;
    }
    public void setValue(String value) {
        this.value = value;
    }
    @Override
        public String toString() {
            return "value="+value;
        }
    @Override
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
    }//因为Object类里的clone方法是protected权限，所以要重写才能在主方法里调用。
}
public class Test_clone {
    public static void main(String[] args) {
        A a1=new A("我是A1");
        A a2=null;
        try {
            a2=(A)a1.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        System.out.println(a1);//value=我是A1
        System.out.println(a2);//value=我是A1
        a1.setValue("a1->A1");
        System.out.println(a1);//value=a1->A1
        System.out.println(a2);//value=我是A1
    }
}