DrawRainbow.java

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package com.mycompany.drawrainbow;

/**
 *
 * @author Monet
 */
 // Fig. 7.25: DrawRainbow.java
 // Demonstrates using colors in an array.
 import java.awt.Color;
 import java.awt.Graphics;
 import javax.swing.JPanel;

 public class DrawRainbow extends JPanel
 {
 // define indigo and violet
 private final static Color VIOLET = new Color( 128, 0, 128 );
 private final static Color INDIGO = new Color( 75, 0, 130 );

 // colors to use in the rainbow, starting from the innermost
 // The two white entries result in an empty arc in the center
 private Color[] colors =
 { Color.WHITE, Color.WHITE, VIOLET, INDIGO, Color.BLUE,
 Color.GREEN, Color.YELLOW, Color.ORANGE, Color.RED };

// constructor
 public DrawRainbow()
 {
 setBackground( Color.WHITE ); // set the background to white
 } // end DrawRainbow constructor
 // draws a rainbow using concentric arcs
 public void paintComponent( Graphics g )
 {

 super.paintComponent( g );

 int radius = 20; // radius of an arc

 // draw the rainbow near the bottom-center
 int centerX = getWidth() / 2;
 int centerY = getHeight() - 10;

 // draws filled arcs starting with the outermost
 for ( int counter = colors.length; counter > 0; counter-- )
 {
    // set the color for the current arc
 g.setColor( colors[ counter - 1 ] );

 // fill the arc from 0 to 180 degrees
 g.fillArc( centerX - counter * radius,
 centerY - counter * radius,
 counter * radius * 2, counter * radius * 2, 0, 180 );
} // end for
 } // end method paintComponent
 } // end class DrawRainbow