Question

I just tried Java Swing helloworld, but I found a question with the following code.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class HelloWorldFrame extends JFrame {

    public static void main(String args[]) {
        new HelloWorldFrame();
    }
    HelloWorldFrame() {

        JButton jbtnButton = new JButton("Button 1");

        jbtnButton.addActionListener(new ActionListener() {

            public void actionPerformed(ActionEvent e) {
                  JOptionPane.showMessageDialog(HelloWorldFrame.this, "You must click at least once!",
                          "Title", JOptionPane.ERROR_MESSAGE);              
            }
        });

        this.add(jbtnButton);

        this.setSize(500, 500);
        // pack();
        setVisible(true);
    }


}

So…my question is simple, how come I don’t need to put return type for “HelloWorldFrame()” ?

Is there a reason or is it just a rule in Java?

Answer 1

Because HelloWorldFrame() is a constructor of the HelloWorldFrame class, and Java constructors, like constructors in most (all?) languages with objects, don’t have return values.