Icons

• Icon

The Icon interface is very simple, specifying just three methods used to determine the size of the Icon and to display it. Implementors of this interface are free to store and display the image in any way.

TestOval.java

The class OvalIcon implements the Icon interface and uses ovals as simple icons.

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

public class TestOval {
  public static void main(String[] args) {
    JFrame f = new JFrame();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JLabel label1 = new JLabel(new OvalIcon(20,50));
    JLabel label2 = new JLabel(new OvalIcon(50,20));
    JLabel label3 = new JLabel
      ("Round!", new OvalIcon(60,60), SwingConstants.CENTER);
    label3.setHorizontalTextPosition(SwingConstants.CENTER);

    Container c = f.getContentPane();
    c.setLayout(new FlowLayout());
    c.add(label1);
    c.add(label2);
    c.add(label3);
    f.pack();
    f.setVisible(true);
  }
}

OvalIcon.java

// OvalIcon.java
//
import javax.swing.*;
import java.awt.*;

// A simple Icon implementation that draws ovals
public class OvalIcon implements Icon {
  public OvalIcon(int w, int h) {
    width = w;
    height = h;
  }

  public void paintIcon(Component c, Graphics g, int x, int y) {
    g.drawOval(x, y, width-1, height-1);
  }

  public int getIconWidth() { return width; }
  public int getIconHeight() { return height; }

  private int width, height;
}

DynamicIconExample.java

Icons are not required to paint themselves the same way every time they are displayed. It's perfectly reasonable (and often quite useful) to have an icon that uses some sort of state information to determine how to display itself. In the following example, two sliders are used to change the width and height of a dynamic icon.

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

// Example of an icon that changes form.
public class DynamicIconExample {
  public static void main(String[] args) {

    // Create a couple sliders to control the icon size
    final JSlider width = new JSlider(JSlider.HORIZONTAL, 1, 150, 75);
    final JSlider height = new JSlider(JSlider.VERTICAL, 1, 150, 75);

    // A little Icon class that uses the current slider values.
    class DynamicIcon implements Icon {
      public int getIconWidth() { return width.getValue(); }
      public int getIconHeight() { return height.getValue(); }
      public void paintIcon(Component c, Graphics g, int x, int y) {
        g.fill3DRect(x, y, getIconWidth(), getIconHeight(), true);
      }
    };
    Icon icon = new DynamicIcon();
    final JLabel dynamicLabel = new JLabel(icon);

    // A listener to repaint the icon when sliders are adjusted.
    class Updater implements ChangeListener {
      public void stateChanged(ChangeEvent ev) {
        dynamicLabel.repaint();
      }
    };
    Updater updater = new Updater();

    width.addChangeListener(updater);
    height.addChangeListener(updater);

    // Lay it all out
    JFrame f = new JFrame();
	f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    Container c = f.getContentPane();
    c.setLayout(new BorderLayout());
    c.add(width, BorderLayout.NORTH);
    c.add(height, BorderLayout.WEST);
    c.add(dynamicLabel, BorderLayout.CENTER);
    f.setSize(210,210);
    f.setVisible(true);
    }
}

Reference: Robert Eckstein, Marc Loy, and Dave Wood, Java Swing, O'Reilly & Associates, 1998, ISBN 1-56592-455-x.

Maintained by John Loomis, last updated 27 July 2000