java - 不要在子类的构造函数中创建父类(super class)实例，但完全合法

Question

我在scjp指南中读到如下内容

In fact, you can't make a new object without invoking not just the constructor of the object's actual class type, but also the constructor of each of its superclasses!

例如

public class Person{

}

public class Employee extends Person{
   public Employee(){
}
}

我没有创建 Person 实例，但它是合法的。

请为我解释一下，谢谢你的帮助。

Answer 1

无论何时实例化一个子类，它都会首先调用父类(super class)的构造函数。

您可以在这里找到更多相关信息:JSL §8.8.7

Person.java

public class Person {
    public Person() {
        System.out.println("Super class constructor called");
    }
}

员工.java

public class Employee extends Person {
    public Employee() {
        System.out.println("Sub class constructor called");
    }
}

如果您随后实例化您的 Employee:

Employee e = new Employee();

输出:

Super class constructor called

Sub class constructor called