The subclass constructor in Java calls the superclass constructor

Say up front:

Every class will have a default constructor (implicit), but if we rewrite a constructor, the default implicit constructor will be overwritten (it will be useless), unless we explicitly define the following , as shown in the following code:

Class Dog(){
    public Dog(){}  //显示声明默认构造器
    public Dog(int age, int weight){}
}

Topic:

Let me talk about the conclusion first: the constructor of the subclass will call the constructor of the parent class first.

 The output of the above code is:

 It can be seen that when we call the subclass constructor to new sonClass, it will first call the parent class constructor, and then call the subclass constructor.