如何将prograssbar的颜色以不同颜色表示?

比方说 进度以20%为一个颜色,也就是100%会有5种颜色(也就是会分成5段不同的颜色),例如:
第一段(0~20%)红色,第二段(20%~40%)橙色,第三段(40%~60%)绿色,第四段(60~80)黄色,第五段(80~100)蓝色

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

class ProgressBarExample
    extends   JFrame
    implements  ActionListener
 {
  private  JProgressBar    progress;
  private  JProgressBar    progress2;
  private  JButton         button;
  private  JLabel          label1;
  private  JPanel          topPanel;

  public ProgressBarExample()
  {
    setTitle( "Progress Bar Application" );
    setSize( 310, 130 );
    setBackground( Color.gray );

    topPanel = new JPanel();
    topPanel.setPreferredSize( new Dimension( 310, 130 ) );
    getContentPane().add( topPanel );

    // Create a label and progress bar
    label1 = new JLabel( "Waiting to start tasks..." );
    label1.setPreferredSize( new Dimension( 280, 24 ) );
    topPanel.add( label1 );

    progress = new JProgressBar();
    progress.setPreferredSize( new Dimension( 300, 20 ) );
    progress.setMinimum( 0 );
    progress.setMaximum( 100 );
    progress.setValue( 0 );
    progress.setBounds( 20, 35, 260, 20 );
    progress2 = new JProgressBar();
    progress2.setPreferredSize( new Dimension( 300, 20 ) );
    progress2.setMinimum( 0 );
    progress2.setMaximum( 100 );
    progress2.setValue( 0 );
    progress2.setBounds( 20, 35, 260, 20 );
  
    topPanel.add( progress );
    topPanel.add( progress2 );

    button = new JButton( "Start" );
    topPanel.add( button );
    button.addActionListener( this );
  }

  public void actionPerformed( ActionEvent event )
  {
    if( event.getSource() == button )
    {
      // Prevent more button presses
      button.setEnabled( false );

      // Perform all of our bogus tasks
      for( int iCtr = 1; iCtr < 101; iCtr++ )
      {
        // Do some sort of simulated task
        DoBogusTask( iCtr );

        // Update the progress indicator and label
        label1.setText( "Performing task " + iCtr + " of 100" );
        Rectangle labelRect = label1.getBounds();
        labelRect.x = 0;
        labelRect.y = 0;
        label1.paintImmediately( labelRect );

        progress.setValue( iCtr );
        Rectangle progressRect = progress.getBounds();
        progressRect.x = 0;
        progressRect.y = 0;
        progress.paintImmediately( progressRect );
        
      }
     }
  }

  public void DoBogusTask( int iCtr )
  {
    Random random = new Random( iCtr );

    // Waste some time
    for( int iValue = 0; iValue < random.nextFloat() * 10000; iValue++ )
    {
      System.out.println( "iValue=" + iValue );
    }
  }

  public static void main( String args[] )
  {
    // Create an instance of the test application
    ProgressBarExample mainFrame  = new ProgressBarExample();
    mainFrame.setVisible( true );
    mainFrame.pack();
  }
}