This Java tip shows how to create a custom icon in Java.

Java Code:
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Graphics;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.AbstractButton;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingConstants;

public class CustomIconDemo extends JPanel implements ActionListener {
  protected JButton b1, b2, b3;

  public CustomIconDemo() {
    Icon leftButtonIcon = new ArrowIcon(SwingConstants.RIGHT);
    Icon middleButtonIcon = new ImageIcon("images/middle.gif");
    Icon rightButtonIcon = new ArrowIcon(SwingConstants.LEFT);

    b1 = new JButton("Disable middle button", leftButtonIcon);
    b1.setVerticalTextPosition(AbstractButton.CENTER);
    b1.setHorizontalTextPosition(AbstractButton.LEFT);
    b1.setMnemonic(KeyEvent.VK_D);
    b1.setActionCommand("disable");

    b2 = new JButton("Middle button", middleButtonIcon);
    b2.setVerticalTextPosition(AbstractButton.BOTTOM);
    b2.setHorizontalTextPosition(AbstractButton.CENTER);
    b2.setMnemonic(KeyEvent.VK_M);

    b3 = new JButton("Enable middle button", rightButtonIcon);
    //Use the default text position of CENTER, RIGHT.
    b3.setMnemonic(KeyEvent.VK_E);
    b3.setActionCommand("enable");
    b3.setEnabled(false);

    //Listen for actions on buttons 1 and 3.
    b1.addActionListener(this);
    b3.addActionListener(this);

    b1.setToolTipText("Click this button to disable the middle button.");
    b2.setToolTipText("This middle button does nothing when you click it.");
    b3.setToolTipText("Click this button to enable the middle button.");

    //Add Components to this container, using the default FlowLayout.
    add(b1);
    add(b2);
    add(b3);
  }

  public void actionPerformed(ActionEvent e) {
    if (e.getActionCommand().equals("disable")) {
      b2.setEnabled(false);
      b1.setEnabled(false);
      b3.setEnabled(true);
    } else {
      b2.setEnabled(true);
      b1.setEnabled(true);
      b3.setEnabled(false);
    }
  }

  public static void main(String[] args) {
    JFrame frame = new JFrame("CustomIconDemo");
    frame.addWindowListener(new WindowAdapter() {
      public void windowClosing(WindowEvent e) {
        System.exit(0);
      }
    });

    frame.getContentPane().add(new CustomIconDemo(), BorderLayout.CENTER);
    frame.pack();
    frame.setVisible(true);
  }
}

class ArrowIcon implements Icon, SwingConstants {
  private int width = 9;

  private int height = 18;

  private int[] xPoints = new int[4];

  private int[] yPoints = new int[4];

  public ArrowIcon(int direction) {
    if (direction == LEFT) {
      xPoints[0] = width;
      yPoints[0] = -1;
      xPoints[1] = width;
      yPoints[1] = height;
      xPoints[2] = 0;
      yPoints[2] = height / 2;
      xPoints[3] = 0;
      yPoints[3] = height / 2 - 1;
    } else /* direction == RIGHT */{
      xPoints[0] = 0;
      yPoints[0] = -1;
      xPoints[1] = 0;
      yPoints[1] = height;
      xPoints[2] = width;
      yPoints[2] = height / 2;
      xPoints[3] = width;
      yPoints[3] = height / 2 - 1;
    }
  }

  public int getIconHeight() {
    return height;
  }

  public int getIconWidth() {
    return width;
  }

  public void paintIcon(Component c, Graphics g, int x, int y) {
    int length = xPoints.length;
    int adjustedXPoints[] = new int[length];
    int adjustedYPoints[] = new int[length];

    for (int i = 0; i < length; i++) {
      adjustedXPoints[i] = xPoints[i] + x;
      adjustedYPoints[i] = yPoints[i] + y;
    }

    if (c.isEnabled()) {
      g.setColor(Color.black);
    } else {
      g.setColor(Color.gray);
    }

    g.fillPolygon(adjustedXPoints, adjustedYPoints, length);
  }
}