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姚屹晨

Java - [面向对象]继承

2020/03/01

本文整理下继承几个有意思的地方。

super

public class Parent {

    public void test(){
        System.out.println("Start test() in Parent");
    }
}

public class Child extends Parent {

    @Override
    public void test(){
        System.out.println("Start test() in Child");
    }
}

@Test
void superTest(){
    Child child = new Child();
    child.test(); // Start test() in Child
}

很明显，调用的是Child类中重写的test()方法。

那么，如何在子类中调用父类的重写方法？

答案就是: super

public class Child extends Parent {

    @Override
    public void test(){
        super.test();
        // System.out.println("Start test() in Child");
    }
}

@Test
void superTest(){
    Child child = new Child();
    child.test(); // Start test() in Parent
}

继承树间构造器的启动顺序

public class Creature {

    public Creature(){
        System.out.println("Default constructor in Creature.");
    }
}

public class Animal extends Creature{

    public Animal(String name){
        System.out.println("The name of animal is " + name);
    }

    public Animal(String name, int age){
        this(name);
        System.out.println(String.format("Age is %d", age));
    }
}

public class Wolf extends Animal {

    public Wolf() {
        super("Wolf", 3);
        System.out.println("Default constructor in Wolf.");
    }
}

@Test
void inheritTreeCreationSeqTest(){
    new Wolf();
}

来猜下构造器的执行顺序。

// Default constructor in Creature.
// The name of animal is Wolf
// Age is 3
// Default constructor in Wolf.

Reference

  • 《疯狂Java讲义》 - 5.6 类的继承


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