Question

Let’s consider this piece of code as our example:

import java.awt.*;

class Maze extends Panel{

    String name;

    public static void main(String[] args){
        Maze m = new Maze();
        System.out.println(m.setName("Hello World").getName());
    }

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

    public String getName(){
        return name;
    }

    public void paint(){

    }
}

I’m trying to understand method chaining, and as what answers said on other questions, use return this. I tried it and yes it works, but not on mutator methods like the method setName() above. Why is the compiler outputting:

The return type is incompatible with Component.setName(String)

Answer 1

Unless Maze derives from some other class that defined setName(String), the Maze setName(String name) signature should be perfectly acceptable

Note: You should write this.name = name;

UPDATE: as it turns out, Maze is deriving from a Panel (which is deriving from Component). As Component.setName(String) specifies its return type as void (void setName(String)), you cannot specify any other return type, but void for setName() in your class. The reason is inheritance: if someone has a reference to your Maze object via a Component reference (e.g. Component c = new Maze();), and calls setName(), the runtime knows to call yours, because of the inheritance. However your version is returning a value, with which the runtime has to do something, but the code is not prepared for it (it was compiled with the knowledge of a Component.