Java子类继承父类构造器

一、研究问题

1.子类如何继承父类的构造器？

2.子类与父类构造器执行顺序？

二、创建父类

创建父类Animal，有两个构造器

class Animal{
    private Integer high;

    public Animal() {
        System.out.println("Animal()");
    }

    public Animal(Integer high) {
        System.out.println("Animal(Integer high)");
        this.high = high;
    }

//    set、get方法
    public Integer getHigh() {
        return high;
    }

    public void setHigh(Integer high) {
        this.high = high;
    }
}

三、创建子类

创建子类Dog，继承Animal，有四个构造器

class Dog extends Animal{
    private String name;

    public Dog() {
        System.out.println("Dog()");
    }

    public Dog(String name) {
        this.name = name;
        System.out.println("Dog(String name)");
    }

    public Dog(Integer high) {
        super(high);
        System.out.println("Dog(Integer high)");
    }

    public Dog(Integer high, String name) {
        super(high);
        this.name = name;
        System.out.println("Dog(Integer high, String name)");
    }

//    set、get方法
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

四、调用子类构造器

public class MyMain {
    public static void main(String[] args) {
        System.out.println("- - - - - - - new Dog() - - - - - - -");
        Dog dog = new Dog();

        System.out.println("- - - - - - - new Dog(Integer high) - - - - - - -");
        Dog highDog = new Dog(180);

        System.out.println("- - - - - - - new Dog(String name) - - - - - - -");
        Dog nameDog  = new Dog("张二狗");

        System.out.println("- - - - - - - new Dog(Integer high, String name) - - - - - - -");
        Dog highNameDog = new Dog(180,"张二狗");

    }
}

五、输出结果

- - - - - - - new Dog() - - - - - - -
Animal()
Dog()
- - - - - - - new Dog(Integer high) - - - - - - -
Animal(Integer high)
Dog(Integer high)
- - - - - - - new Dog(String name) - - - - - - -
Animal()
Dog(String name)
- - - - - - - new Dog(Integer high, String name) - - - - - - -
Animal(Integer high)
Dog(Integer high, String name)

六、结论

1.子类通过super调用父类构造器

子类通过super()调用父类无参构造器；通过super(参数)调用父类有参构造器；如果不写super，子类默认调用父

类无参构造器

2.子类创建对象时，父类构造器会先执行。

因为在构造器中super必须放在第一个执行，否则会报错