JButton

We will discuss JButton is this lecture. You should refer to JButton

JButton's useful methods

The following tables list the commonly used button-related API.

Setting or Getting the Button's Contents
Method or Constructor Purpose
JButton(String, Icon)
JButton(String)
JButton(Icon)
JButton() 		Create a JButton instance, initializing it to have the specified text/image.
void setText(String)
String getText() 		Set or get the text displayed by the button.
void setIcon(Icon)
Icon getIcon() 		Set or get the image displayed by the button when the button isn't selected or pressed.
void setDisabledIcon(Icon)
Icon getDisabledIcon() 		Set or get the image displayed by the button when it's disabled. If you don't specify a disabled image, then the look and feel creates one by manipulating the default image.
void setPressedIcon(Icon)
Icon getPressedIcon() 		Set or get the image displayed by the button when it's being pressed.
setRolloverEnabled(boolean)
boolean getRolloverEnabled()
void setRolloverIcon(Icon)
Icon getRolloverIcon()
void setRolloverSelectedIcon(Icon)
Icon getRolloverSelectedIcon() 		Use setRolloverEnabled(true) and setRolloverIcon(someIcon) to make the button display the specified icon when the cursor passes over it.

Fine Tuning the Button's Appearance
Method or Constructor Purpose
void setHorizontalAlignment(int)
void setVerticalAlignment(int)
int getHorizontalAlignment()
int getVerticalAlignment() 		Set or get where in the button its contents should be placed. The AbstractButton class allows any one of the following values for horizontal alignment: LEFT, CENTER (the default), and RIGHT. For vertical alignment: TOP, CENTER (the default), and BOTTOM.
void setHorizontalTextPosition(int)
void setVerticalTextPosition(int)
int getHorizontalTextPosition()
int getVerticalTextPosition() 		Set or get where the button's text should be placed, relative to the button's image. The AbstractButton class allows any one of the following values for horizontal position: LEFT, CENTER, and RIGHT (the default). For vertical position: TOP, CENTER (the default), and BOTTOM.

Question

Create a class DogButton extends JButton with the following icons
doggie1.gif
icon
filename : doggie1.gif		 doggie2.gif
icon when you roll over(move mouse onto) the button.
filename : doggie2.gif		 doggie3.gif
icon when you press the button.
filename : doggie3.gif

DogButtonTest.java

Here is an example on how to use the DogButton class. You can get the program here.
dogbuttona.gif
normal look		 dogbuttonb.gif
move mouse on the button. 		dogbuttonc.gif
press the button. 
   1:import java.awt.*;
   2:import javax.swing.*;
   3:
   4:public class DogButtonTest{
   5:    public static void main(String[] args) {
   6:        JFrame f = new JFrame();
   7:        f.getContentPane().add(new DogButton());
   8:        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
   9:        f.setTitle("Dog");
  10:        f.setSize(100,80);
  11:        f.setVisible(true);
  12:    }
  13:}
See how we use the constructor at line 7.

Answer : DogButton.java

You can get the program here.
Remember to save the pictures by right clicking on the pictures and select "save image". 
   1:import java.awt.*;
   2:import javax.swing.*;
   3:
   4:public class DogButton extends JButton {
   5:    private Icon icon = new ImageIcon("doggie1.gif");
   6:    private Icon rolloverIcon = new ImageIcon("doggie2.gif");
   7:    private Icon pressedIcon = new ImageIcon("doggie3.gif");
   8:    public DogButton() {
   9:        setIcon(icon);
  10:        setRolloverIcon(rolloverIcon);
  11:        setPressedIcon(pressedIcon);
  12:    }   
  13:}
What is wrong if I replace the constructor by 
public DogButton() {
        super(icon);
        setRolloverIcon(rolloverIcon);
        setPressedIcon(pressedIcon);
}
Answer: super(icon) is the first line to be called. But at that point of the program, icon hasn't been declared yet.

Button with action

We are going to write a program react to user's clicks. The class extends JFrame, when you click on the button, the counter increase by 1.
You can get the program here.
buttontest.gif
Don't worry if you don't really understand the program. We will discuss the concept in more detail later. 
   1:import java.awt.*;
   2:import javax.swing.*;
   3:import java.awt.event.*; 
   4:
   5:public class ButtonTest extends JFrame implements ActionListener {
   6:    private JLabel countLabel;
   7:    private JButton button;
   8:    private int count = 0; 
   9:    private Container contentPane;
  10:    public ButtonTest() {
  11:        contentPane = getContentPane();
  12:        contentPane.setLayout(new GridLayout(2,1));
  13:        // change the count to string. alignment is center
  14:        countLabel = new JLabel(Integer.toString(count), JLabel.CENTER);
  15:        button = new JButton("Click me");
  16:        contentPane.add(countLabel);
  17:        contentPane.add(button);
  18:        // the class is an action listener
  19:        button.addActionListener(this);
  20:    }
  21:    
  22:    // what happens after you click the button
  23:    public void actionPerformed(ActionEvent e) {
  24:        count++;
  25:        countLabel.setText(Integer.toString(count));
  26:    }
  27:    
  28:   public static void main(String[] args) {
  29:        ButtonTest f = new ButtonTest();
  30:        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  31:        f.pack();
  32:        f.setVisible(true);
  33:    }
  34:}

Highlight of the program

Line 5 : implements has almost the exact meaning as extends. We have to override actionPerformed method inherited from the class ActionListener.
Line 19 : addActionListener to the button. ButtonTest "extends" ActionListener, so it itself is an ActionListener.
Line 23 - Line 26 : actionPerformed method. Describe the reaction of the class when the user clicks on it.