Java: Example - ColorDisplay

In this example code we will show you how to make ColorDisplay application using Swing framework.

This example shows color set by RGB scrollbars.

In the main method of the example code we are doing following things:

Creating object of ColorDisplay class as shown below:

 JFrame window = new ColorDisplay();

Setting the Default Close Operation

window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

Finally displaying the window:

window.setVisible(true);

The GraphicsPanel class is also used in the example.

GraphicsPanel palette;

The following code listing provides you complete code:

/*****************************************************
  * Shows color set by RGB scrollbars.
  * @version One of my first Java programs (1995?), last update 2002-04-21.
  * @author Fred Swartz
  */

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

////////////////////////////////////////////////////////////////// ColorDisplay
class ColorDisplay extends JFrame {

    JSlider redBar; // Slider for adjusting red from 0-255
    JSlider grnBar;
    JSlider bluBar;

    int red   = 128; // initial red color value
    int green = 128;
    int blue  = 128;

    GraphicsPanel palette; // an area to display the color
    JTextField txtField;   // shows the Java source equivalent

    //================================================ constructor
    public ColorDisplay() {
        palette = new GraphicsPanel();

        // Create a textfield for displaying the values
        txtField = new JTextField();
        txtField.setFont(new Font("Monospaced", Font.PLAIN, 12));
        txtField.setText("Color(" + red + ", " + green + ", " + blue +
                ") or " + "Color(0x" + 
                Integer.toHexString(blue + 256 * (green + 256 * red)) + ")");
        txtField.setEditable(false);

        // Create one object that will listen to all sliders
        ChangeListener al = new ColorListener();

        redBar = new JSlider(JSlider.VERTICAL, 0, 255, red);
        redBar.addChangeListener(al);
        redBar.setBackground(Color.red);

        grnBar = new JSlider(JSlider.VERTICAL, 0, 255, green);
        grnBar.addChangeListener(al);
        grnBar.setBackground(Color.green);

        bluBar = new JSlider(JSlider.VERTICAL, 0, 255, blue);
        bluBar.addChangeListener(al);
        bluBar.setBackground(Color.blue);

        //=== Put the color palette and textfield in a box
        Box paletteText = Box.createVerticalBox();
        paletteText.add(palette);
        paletteText.add(txtField);

        //=== put the 3 sliders in a gridlayout panel
        JPanel colorControls = new JPanel();
        colorControls.setLayout(new GridLayout(1, 3));
        colorControls.add(redBar);
        colorControls.add(grnBar);
        colorControls.add(bluBar);
        
        //=== Now let's build the content pane
        Container content = this.getContentPane();
        content.setLayout(new BoxLayout(content, BoxLayout.X_AXIS));
        content.add(paletteText);
        content.add(colorControls);
        
        this.setTitle("ColorDisplay");
        this.pack();
    }//end constructor
    
////////////////////////////////////////////////////////////// GraphicsPanel
        // A component for drawing ,overrides paintComponent()
    class GraphicsPanel extends JPanel {
        //======================================== GraphicsPanel constructor
        public GraphicsPanel() {
            this.setPreferredSize(new Dimension(300, 300));
            this.setBackground(Color.white);
            this.setForeground(Color.black);
        }//end constructor

        //=================================== GraphicsPanel : paintComponent
        public void paintComponent(Graphics g) {
            super.paintComponent(g);           // paint background, border
            g.setColor(new Color(red, green, blue)); // Set the color
            g.fillRect(0, 0, this.getWidth(), this.getHeight()); // Color everything
        }//endmethod paintComponent
    }//endclass GraphicsPanel

    
    ///////////////////////////////////////////////////// class ColorListener
        // This class is created only as a place to put the listener.
        // We could have just as easily put the listener in any other class,
        // or used an anonymous listener.
        // This is defined as an inner class (defined inside of ColorDisplay),
        // so it can reference the field variables of that class (specifically,
        // the sliders, graphics panel, and text field).
    class ColorListener implements ChangeListener {
        public void stateChanged(ChangeEvent ae) {
            red   = redBar.getValue();
            green = grnBar.getValue();
            blue  = bluBar.getValue();
            txtField.setText("Color(" + red + ", " + green + ", " + blue +
                    ") or " + "Color(0x" + Integer.toHexString(blue +
                    256 * (green + 256 * red)) + ")");
            palette.repaint();
        }//endmethod stateChanged
    }//endclass ColorListener
    
    //================================================================= main
    public static void main(String[] args) {
        JFrame window = new ColorDisplay();
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        window.setVisible(true);
    }//end main

}//end class ColorDisplay

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