Question

当使用来自二级子类的超类构造函数时，它是否将参数传递给祖父项构造函数或直接父构造函数？

//top class
public First(type first){
  varFirst = first;
}

//child of First
public Second(type second){
  super(second); //calls First(second)
}

//child of Second
public Third(type third){
  super(third); //calls First(third) or Second(third)?
}

Answer 1

super调用直接父级的构造函数。因此，super中的Third电话会调用Second的构造函数，而构造函数又调用First。如果在构造函数中添加一些print语句，这很容易看到：

public class First {
    public First(String first) {
        System.out.println("in first");
    }
}

public class Second extends First {
    public Second(String second) {
        super(second);
        System.out.println("in second");
    }
}

public class Third extends Second {
    public Third(String third) {
        super(third);
        System.out.println("in third");
    }

    public static void main(String[] args) {
        new Third("yay!");
    }
}

您获得的输出：

in first
in second
in third

Answer 2

super in Child尝试从Parent获取信息，而Parent中的super尝试从GrandParent获取信息。

    public class Grandpapa {

    public void display() {
        System.out.println(" Grandpapa");
    }

    static class Parent extends Grandpapa{
        public void display() {
            super.display();
            System.out.println("parent");
        }
    }

    static class Child extends Parent{
        public void display() {
        //  super.super.display();// this will create error in Java
            super.display();
            System.out.println("child");
        }
    }

    public static void main(String[] args) {
            Child cc = new Child();
            cc.display();
 /*
            * the output :
                 Grandpapa
                 parent
                 child
            */
    }
}

从孙子类调用超类构造函数，调用父或祖父项构造函数？

2 个答案: