Extending a java class whilst also altering it

Question

I've been a lurker on stackoverflow for some time. I'm teaching myself Java, so bear with me if this is a rather elementary question (I couldn't find the answer on here though).

If I have a java class (like the one below), which I wish to use in future classes in a slightly different way (e.g. changing the button text/or output), is there a way to do this by extending the original class?

In the case below I have a JFrame with two buttons which print different text to the console. I simply want to extend this class whilst changing one of the button names.

ORIGINAL CLASS:

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;

public class FrameIt extends JFrame implements ActionListener {

    private static final long serialVersionUID = 1L;

    public static void main(String[] args) {
        new FrameIt().setVisible(true);
    }

    public FrameIt() {
        super("Make a choice");
        setSize(600, 600);
        setResizable(false);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLayout(new GridLayout());

        JButton button = new JButton("Click Me.");
        JButton button2 = new JButton("No, you should Click Me!");
        button.addActionListener(this);
        button2.addActionListener(this);

        add(button);
        add(button2);
    }

    @Override

    public void actionPerformed(ActionEvent e) {
        String name = e.getActionCommand();
        if(name.equals("Click Me")){
            System.out.println("That was actually the right choice.");
        }else{
            System.out.println("Poor choice.");
        }
    }
}

CLASS THAT EXTENDS:

import javax.swing.JButton;

public class Alterations extends FrameIt{

    private static final long serialVersionUID = 1L;

    public static void main(String args[]){
        new Alterations().setVisible(true);
        System.out.println("Doing it");
    }

    public Alterations(){
        JButton button2 = new JButton("Slightly different button");

    }
}

Thanks.

There's no need for inheritance for this. Just provide an additional constructor taking the button name as argument, and using that name instead of the default one. — JB Nizet, Jul 12 '15 at 08:34

score 0 · Accepted Answer · answered Jul 12 '15 at 08:36

Creating the JButton instance in the sub-class Alterations will make no difference, since you don't connect it to anything.

One way to handle it is to change the constructor of the original class. You can make the name of the button originate from a method call :

Change :

JButton button2 = new JButton("No, you should Click Me!");

To :

JButton button2 = new JButton(getSecondButtonName ());

Then getSecondButtonName() can return "No, you should Click Me!" in the original class and you can override it in the sub-class to return "Slightly different button".

An alternative would be to remove the original button in the constructor of the sub-class and add the new button.

These solutions make sense only if there's a real reason to create a sub-class in the first place. If the only difference between the base class and the sub-class is the name of one button, there's no reason to create a sub-class.

Brilliant. Here are the other lines of code I used to make it work: Original class: `public String getSecondButtonName() { return "Initial"; }` Extending class: `public String getSecondButtonName() { return "ALTERED"; }` — Pineapple, Jul 12 '15 at 11:18

Extending a java class whilst also altering it

1 Answers1