Constructor of Super and Sub

This compilation error occurs because the default super constructor is undefined. In Java, if a class does not define a constructor, compiler will insert a default no-argument constructor for the class by default. If a constructor is defined in Super class, in this case Super(String s), compiler will not insert the default no-argument constructor. This is the situation for the Super class above.

The constructors of the Sub class, either with-argument or no-argument, will call the no-argument Super constructor. Since compiler tries to insert super() to the 2 constructors in the Sub class, but the Super's default constructor is not defined, compiler reports the error message.

To fix this problem, simply 1) add a Super() constructor to the Super class like

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

, or 2) remove the self-defined Super constructor, or 3) add super(value) to sub constructors.