ActionListener

[Kid Programmer]

Hello guys. How do you create an ActionListener. I am confused on how to do it.
Here is my code:

/**
 * Written By: Edward Sanger
 * Coded in: Java
 * IDE Used: IntelliJ IDEA
 * Program Name: Calculator
 * Program Description: This program will create a GUI window with 4 buttons for 4 mathematical operators and 2 text
 * fields for the numbers to add, subtract, multiply, and divide.
 * Date: May 26, 2008
 * Time: 2:34:52 PM
 */
 
//import declarations
import java.awt.*;
import javax.swing.*;
 
public class Calculator implements ActionListener {
    public static void main(String[] args) {
        //create a new jframe
        JFrame frame = new JFrame();
        frame.setTitle("Calculator");
        //create a container
        Container contentPane = frame.getContentPane();
 
        //create the frame objects
        JTextField num1 = new JTextField("Number 1");
        JTextField num2 = new JTextField("Number 2");
 
        JButton add = new JButton("Add");
        JButton subtract = new JButton("Subtract");
        JButton multiply = new JButton("Multiply");
        JButton divide = new JButton("Subtract");
 
        JLabel result = new JLabel("Result");
 
        //add the objects
        contentPane.add(num1);
        contentPane.add(num2);
 
        contentPane.add(add);
        contentPane.add(subtract);
        contentPane.add(multiply);
        contentPane.add(divide);
 
        contentPane.add(result);
 
        //create the layout
        FlowLayout layout = new FlowLayout();
        contentPane.setLayout(layout);
 
        //create an action listener
 
 
        //frame settings
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setVisible(true);
    }
}
 

[BigDaddyLH]

Did you look in the new tutorial?

http://java.sun.com/docs/books/tutor...nlistener.html

[Kid Programmer]

Did you look in the new tutorial?

http://java.sun.com/docs/books/tutor...nlistener.html

2 questions.

1. What goes in the parentheses in this line of code

b.addActionListener(this);

2. In my code I have four buttons. How do I create a seperate event for each one. It just says in the tutorial:

public void actionPerformed(ActionEvent e) {

[BigDaddyLH]

2 questions.

1. What goes in the parentheses in this line of code

b.addActionListener(this);

2. In my code I have four buttons. How do I create a seperate event for each one. It just says in the tutorial:

public void actionPerformed(ActionEvent e) {

1. To find out how to use a method, look it up in the API:

void addActionListener(ActionListener listener)

So you pass addActionListener a reference to an ActionListener.

2. Separate events? The buttons create the events. I think you mean "separate event listeners". You create separate listeners by creating separate listeners. I think you are confused about something, because that question is like asking "how can I define four classes" or "how can I eat four apples". You go ahead and do it. Here's a quick demo:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
class Listener1 implements ActionListener {
    public void actionPerformed(ActionEvent evt) {
        System.out.println("Listener1");
    }
}
 
class Listener2 implements ActionListener {
    public void actionPerformed(ActionEvent evt) {
        System.out.println("Listener2");
    }
}
 
class Listener3 implements ActionListener {
    public void actionPerformed(ActionEvent evt) {
        System.out.println("Listener3");
    }
}
 
class Listener4 implements ActionListener {
    public void actionPerformed(ActionEvent evt) {
        System.out.println("Listener4");
    }
}
 
public class FourListenersExample {
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable(){
            public void run() {
                launch();
            }
        });
    }
 
    static void launch() {
        JPanel cp = new JPanel();
        configure(cp, "button 1", new Listener1());
        configure(cp, "button 2", new Listener2());
        configure(cp, "button 3", new Listener3());
        configure(cp, "button 4", new Listener4());
 
        JFrame f = new JFrame("FourListenersExample");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setContentPane(cp);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
 
    static void configure(JPanel cp, String text, ActionListener al) {
        JButton btn = new JButton(text);
        btn.addActionListener(al);
        cp.add(btn);
    }
}

[Kid Programmer]

1. To find out how to use a method, look it up in the API:

void addActionListener(ActionListener listener)

So you pass addActionListener a reference to an ActionListener.

2. Separate events? The buttons create the events. I think you mean "separate event listeners". You create separate listeners by creating separate listeners. I think you are confused about something, because that question is like asking "how can I define four classes" or "how can I eat four apples". You go ahead and do it. Here's a quick demo:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
class Listener1 implements ActionListener {
    public void actionPerformed(ActionEvent evt) {
        System.out.println("Listener1");
    }
}
 
class Listener2 implements ActionListener {
    public void actionPerformed(ActionEvent evt) {
        System.out.println("Listener2");
    }
}
 
class Listener3 implements ActionListener {
    public void actionPerformed(ActionEvent evt) {
        System.out.println("Listener3");
    }
}
 
class Listener4 implements ActionListener {
    public void actionPerformed(ActionEvent evt) {
        System.out.println("Listener4");
    }
}
 
public class FourListenersExample {
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable(){
            public void run() {
                launch();
            }
        });
    }
 
    static void launch() {
        JPanel cp = new JPanel();
        configure(cp, "button 1", new Listener1());
        configure(cp, "button 2", new Listener2());
        configure(cp, "button 3", new Listener3());
        configure(cp, "button 4", new Listener4());
 
        JFrame f = new JFrame("FourListenersExample");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setContentPane(cp);
        f.pack();
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }
 
    static void configure(JPanel cp, String text, ActionListener al) {
        JButton btn = new JButton(text);
        btn.addActionListener(al);
        cp.add(btn);
    }
}

I am getting errors in my code for the methods. It says Identifier expected.