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

Yes, that is the right idea. You must do two things in order to be able to do that, though:

1. Put this at the beginning of the FInput class:

   Main m = new Main(this);
   

2. Then, put these lines somewhere in the Main class...

   FInput gui;
   
   public Main(FInput in) { gui = in; }
   

Now you can refer to any component in the FInput class from the Main class by doing something like this.

gui.someComponent ...

To set up listeners just write someComponent.addItemListener(m); or something of the sort.

Hope this helps!

---

@Yoav In response to your latest comment...

You don't have to separate the listening class from the GUI class; you can combine the two into one class...

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

public class Main extends JFrame implements ActionListener {

    private JTextField txtSourceDirectory;
    private JTextField txtTargetDirectory;
    private JTextField txtDefectNumber;
    private JTextField txtSliceTokens;
    private JButton btnStart;

    public Main() {
        txtSourceDirectory = new JTextField(40); //change this to the amount of characters you need
        txtTargetDirectory = new JTextField(40);
        txtDefectNumber = new JTextField(40);
        txtSliceTokens = new JTextField(40);
        btnStart = new JButton("Start");
        add(txtSourceDirectory);
        add(txtTargetDirectory);
        add(txtDefectNumber);
        add(txtSliceTokens);
        add(btnStart);
        btnStart.addActionListener(this);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        pack();
        setVisible(true);
    }

    public void actionPerformed(ActionEvent event) {
        //do stuff
    }

    static void startProcess(String[] ARGS) {
        //do stuff
    }

    public static void main(String[] args) {
        if (args.length == 0) {
            Main frame = new Main();
        } else {
            startProcess(args);
        }
    }
}

Answer 2

Also consider using JOptionPane, shown here, in your Main class. You can customize the appearance, including button text, as shown in How to Make Dialogs.

Answer 3

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
    }
}