action notes 4

More examples on ActionListener

ColorButton1.java

3 buttons have 3 different colors (red, blue, green).
when you click on any button, the label is changed to the background color of the button.

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

public class ColorButton1 extends JFrame implements ActionListener {
    private JButton[] buttons = new JButton[3]; // 3 buttons with color
    private JLabel label = new JLabel();  
    private Container contentPane = getContentPane();
    private JPanel northPanel = new JPanel(new GridLayout(1,0)); // 1 row
    public ColorButton1() {
        buttons[0] = new JButton();
        buttons[0].setBackground(Color.red);
        buttons[0].setActionCommand("red");
        buttons[0].addActionListener(this);
        northPanel.add(buttons[0]);
        buttons[1] = new JButton();
        buttons[1].setBackground(Color.blue);
        buttons[1].setActionCommand("blue");
        buttons[1].addActionListener(this);
        northPanel.add(buttons[1]);
        buttons[2] = new JButton();
        buttons[2].setBackground(Color.green);
        buttons[2].setActionCommand("green");
        buttons[2].addActionListener(this);
        northPanel.add(buttons[2]);
        // set a bigger size of northPanel
        northPanel.setPreferredSize(new java.awt.Dimension(300,50));
        
        label.setOpaque(true);
        
        contentPane.add(northPanel, BorderLayout.NORTH);
        contentPane.add(label);
    }
    
    public void actionPerformed(ActionEvent e) {
        String color = e.getActionCommand();
        if(color.equals("red")) {
            label.setBackground(Color.red);
        } else if(color.equals("blue")) {
            label.setBackground(Color.blue);
        } else if(color.equals("green")) {
            label.setBackground(Color.green);
        }
    }
    
    public static void main(String[] args) {
         JFrame f = new ColorButton1();
         f.setSize(300,150);
         f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         f.setVisible(true);
         
    }
}

use setActionCommand(String actionCommand)
use e.getActionCommand() to find out which button you click

ColorButton2.java

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

public class ColorButton2 extends JFrame implements ActionListener {
    private JButton[] buttons = new JButton[3]; // 3 buttons with color
    private JLabel label = new JLabel();  
    private Container contentPane = getContentPane();
    private JPanel northPanel = new JPanel(new GridLayout(1,0)); // 1 row
    public ColorButton2() {
        buttons[0] = new JButton();
        buttons[0].setBackground(Color.red);
        buttons[0].addActionListener(this);
        northPanel.add(buttons[0]);
        buttons[1] = new JButton();
        buttons[1].setBackground(Color.blue);
        buttons[1].addActionListener(this);
        northPanel.add(buttons[1]);
        buttons[2] = new JButton();
        buttons[2].setBackground(Color.green);
        buttons[2].addActionListener(this);
        northPanel.add(buttons[2]);
        // set a bigger size of northPanel
        northPanel.setPreferredSize(new java.awt.Dimension(300,50));
        
        label.setOpaque(true);
        
        contentPane.add(northPanel, BorderLayout.NORTH);
        contentPane.add(label);
    }
    
    public void actionPerformed(ActionEvent e) {
        if(e.getSource() == buttons[0]) {
            label.setBackground(Color.red);
        } else if(e.getSource() == buttons[1]) {
            label.setBackground(Color.blue);
        } else if(e.getSource() == buttons[2]) {
            label.setBackground(Color.green);
        }
    }
    
    public static void main(String[] args) {
         JFrame f = new ColorButton2();
         f.setSize(300,150);
         f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         f.setVisible(true);
         
    }
}

use e.getSource() to find out which button you click.
compare them by e.getSource() == button[i].

ColorButton3.java

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

public class ColorButton3 extends JFrame implements ActionListener {
    private JButton[] buttons;
    private Color[] colors = {Color.red, Color.blue, Color.green, Color.yellow, Color.pink};
    private JLabel label = new JLabel();  
    private Container contentPane = getContentPane();
    private JPanel northPanel = new JPanel(new GridLayout(1,0)); // 1 row
    public ColorButton3() {
        buttons = new JButton[colors.length];
        for(int i = 0; i < buttons.length; i++) {
            buttons[i] = new JButton();
            buttons[i].setBackground(colors[i]);
            buttons[i].addActionListener(this);
            northPanel.add(buttons[i]);
        }

        // set a bigger size of northPanel
        northPanel.setPreferredSize(new java.awt.Dimension(300,50));
        
        label.setOpaque(true);
        
        contentPane.add(northPanel, BorderLayout.NORTH);
        contentPane.add(label);
    }
    
    public void actionPerformed(ActionEvent e) {
        // e.getSource() returns Component
        // type casting to JButton
        JButton button = (JButton)e.getSource();
        Color color = button.getBackground(); 
        label.setBackground(color);
    }
    
    public static void main(String[] args) {
         JFrame f = new ColorButton3();
         f.setSize(300,150);
         f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         f.setVisible(true);
         
    }
}

Use (JButton)e.getSource() to get the button you click.
e.getSource() returns Component
type casting

ColorButton4.java

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

public class ColorButton4 extends JFrame {
    private JButton[] buttons = new JButton[3]; // 3 buttons with color
    private JLabel label = new JLabel();  
    private Container contentPane = getContentPane();
    private JPanel northPanel = new JPanel(new GridLayout(1,0)); // 1 row
    public ColorButton4() {
        buttons[0] = new JButton();
        buttons[0].setBackground(Color.red);
        buttons[0].addActionListener(
              new ActionListener() {
                  public void actionPerformed(ActionEvent e) {
                      label.setBackground(Color.red);
                  }
              }
        );
        northPanel.add(buttons[0]);
        buttons[1] = new JButton();
        buttons[1].setBackground(Color.blue);
        buttons[1].addActionListener(
              new ActionListener() {
                  public void actionPerformed(ActionEvent e) {
                      label.setBackground(Color.blue);
                  }
              }
        );
        northPanel.add(buttons[1]);
        buttons[2] = new JButton();
        buttons[2].setBackground(Color.green);
        buttons[2].addActionListener(
              new ActionListener() {
                  public void actionPerformed(ActionEvent e) {
                      label.setBackground(Color.green);
                  }
              }
        );
        northPanel.add(buttons[2]);
        // set a bigger size of northPanel
        northPanel.setPreferredSize(new java.awt.Dimension(300,50));
        
        label.setOpaque(true);
        
        contentPane.add(northPanel, BorderLayout.NORTH);
        contentPane.add(label);
    }
    
    
    public static void main(String[] args) {
         JFrame f = new ColorButton4();
         f.setSize(300,150);
         f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         f.setVisible(true);
         
    }
}

anonymous class
you can access members of the class

ColorButton5.java

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

public class ColorButton5 extends JFrame {
    private JButton[] buttons;
    private Color[] colors = {Color.red, Color.blue, Color.green, Color.yellow,  Color.pink};
    private JLabel label = new JLabel();  
    private Container contentPane = getContentPane();
    private JPanel northPanel = new JPanel(new GridLayout(1,0)); // 1 row
    
    public ColorButton5() {
       buttons = new JButton[colors.length];
        for(int i = 0; i < buttons.length; i++) {
            buttons[i] = new JButton();
            buttons[i].setBackground(colors[i]);
            buttons[i].addActionListener(new Listener());
            northPanel.add(buttons[i]);
        }
        // set a bigger size of northPanel
        northPanel.setPreferredSize(new java.awt.Dimension(300,50));
        
        label.setOpaque(true);
        
        contentPane.add(northPanel, BorderLayout.NORTH);
        contentPane.add(label);
    }
    
    public static void main(String[] args) {
         JFrame f = new ColorButton5();
         f.setSize(300,150);
         f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         f.setVisible(true);
         
    }
    
    // inner class
    class Listener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
            Color color = ((JButton)e.getSource()).getBackground();
            label.setBackground(color);
        }
    }   
}

inner class : a class inside class body.
you can access members of the class

ColorButton6.java

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

public class ColorButton6 extends JFrame {
    private JButton[] buttons;
    private Color[] colors = {Color.red, Color.blue, Color.green, Color.yellow,  Color.pink};
    protected JLabel label = new JLabel();  
    private Container contentPane = getContentPane();
    private JPanel northPanel = new JPanel(new GridLayout(1,0)); // 1 row
    
    public ColorButton6() {
       buttons = new JButton[colors.length];
        for(int i = 0; i < buttons.length; i++) {
            buttons[i] = new JButton();
            buttons[i].setBackground(colors[i]);
            buttons[i].addActionListener(new Listener(this));
            northPanel.add(buttons[i]);
        }
        // set a bigger size of northPanel
        northPanel.setPreferredSize(new java.awt.Dimension(300,50));
        
        label.setOpaque(true);
        
        contentPane.add(northPanel, BorderLayout.NORTH);
        contentPane.add(label);
    }
    
    public static void main(String[] args) {
         JFrame f = new ColorButton6();
         f.setSize(300,150);
         f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         f.setVisible(true);
         
    }
}    

    // inner class
class Listener implements ActionListener {
    ColorButton6 colorButton;
    public Listener(ColorButton6 colorButton) {
        this.colorButton = colorButton;
    }
    
    public void actionPerformed(ActionEvent e) {
          Color color = ((JButton)e.getSource()).getBackground();
          colorButton.label.setBackground(color);
   }
}

create a new class.
pass the class as a member.
change private JLabel label to protected JLabel label so that the listener can access the member.