Handle JButton click event in another class

Question

I\'m new to java coming from C# so I\'m not familiar with java best practices.

I have a main class that opens a JFrame to get several input strings from a user. When

Answer 1

First main method in java always must be public static void. Below is example how this can be done.

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

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

/**
 * Main class is frame but also implements ActionListener interface.
 */
public class Main extends JFrame implements ActionListener {
    private JButton btnStart;
    private static Main frame;

    public Main() {
        JPanel panel = new JPanel();
        btnStart = new JButton("Press me");

        // Add action listener. Listener could be any class that implements
        // ActionListener
        btnStart.addActionListener(this);

        // This means add button btnStart to panel
        panel.add(btnStart);

        // This means add panel to frame
        this.add(panel);
    }

    // main method in java always must be public, static and void. You forgot to
    // put static.
    public static void main(String[] args) {
        if (args.length == 0) {
            frame = new Main();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.pack();
            frame.setVisible(true);
        } else
            frame.startProcess(args);
    }

    public void startProcess(String[] args) {
        // TODO
    }

    @Override
    public void actionPerformed(ActionEvent arg0) {
        // Here you put your code that is executed every time you press button.
        // For example you just want to show message.
        JOptionPane.showMessageDialog(this, "You pressed Button.");

    }
}

But it is much better to have special class. For example:

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

import javax.swing.JFrame;
import javax.swing.JOptionPane;


    public class ButtonListener implements ActionListener {
        JFrame parent;

        public ButtonListener(JFrame parent) {
            this.parent = parent;
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            JOptionPane.showMessageDialog(parent, "You pressed Button");
        }

    }

And in the main class you just add action listener to button:

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

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextField;

/**
 * Main class is frame but also implements ActionListener interface.
 */
public class Main extends JFrame {
    private JButton btnStart;
    private static Main frame;

    public Main() {
        JPanel panel = new JPanel();
        btnStart = new JButton("Press me");


        ButtonListener listener = new ButtonListener(this);
        // Add action listener. Listener could be any class that implements
        // ActionListener
        btnStart.addActionListener(listener);

        // This means add button btnStart to panel
        panel.add(btnStart);

        // This means add panel to frame
        this.add(panel);
    }

    // main method in java always must be public, static and void. You forgot to
    // put static.
    public static void main(String[] args) {
        if (args.length == 0) {
            frame = new Main();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.pack();
            frame.setVisible(true);
        } else
            frame.startProcess(args);
    }

    public void startProcess(String[] args) {
        // TODO
    }
}