java - 什么时候在下面的代码中调用 super()

Question

试图了解何时调用 super() 方法。在下面的代码中，Child 类有一个带有 this() 的无参数构造函数，因此编译器无法插入 super()。那么父构造函数是如何调用的。

public class Parent
{
    public Parent()
    {
        System.out.println("In parent constructor");
    }
 }


public class Child extends Parent
{
private int age;

public Child()
{   
    this(10);
    System.out.println("In child constructor with no argument");
}

public Child(int age)
{
    this.age = age;
    System.out.println("In child constructor with argument");
}

public static void main(String[] args)
{
    System.out.println("In main method");
    Child child = new Child();
}

}

输出:

In main method

In parent constructor

In child constructor with argument

In child constructor with no argument

Answer 1

这是发生了什么:

public class Parent
{
    public Parent()
    {
        System.out.println("In parent constructor"); // 4 <------
    }
}


public class Child extends Parent
{
    private int age;

    public Child()
    {
        this(10); // 2 <------
        System.out.println("In child constructor with no argument"); // 6 <------
    }

    public Child(int age)
    {
        // 3 -- implicit call to super()  <------
        this.age = age;
        System.out.println("In child constructor with argument"); // 5 <------
    }

    public static void main(String[] args)
    {
        System.out.println("In main method"); // 1 <------
        Child child = new Child();
    }
}