import java.awt.BorderLayout;

import java.awt.Color;

import java.awt.GradientPaint;

import java.awt.Graphics;

import java.awt.Graphics2D;

import java.awt.LayoutManager;

 

import javax.swing.JFrame;

import javax.swing.JPanel;

import javax.swing.WindowConstants;

 

public class GradientPanel extends JPanel {

 

    public GradientPanel(LayoutManager lm) {

        super(lm);

    }

    public void paintComponent(Graphics g) {

        super.paintComponent(g);

        if (!isOpaque()) {

            return;

        }

       

        int width = getWidth();

        int height = getHeight();

        Graphics2D g2 = (Graphics2D) g;

        GradientPaint gradientPaint =new GradientPaint(0, 0, Color.blue, width/2, height/2,Color.red,false);

       

       

        g2.setPaint(gradientPaint);

        g2.fillRect(0, 0, width, height);

       

    }

   

   

    public static void main(String args[]){

           JFrame jf=new JFrame("GradientPanelTest");

           jf.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

           GradientPanel gp=new GradientPanel(new BorderLayout());

           jf.getContentPane().add(gp);

           jf.setSize(500,400);

           jf.setVisible(true);

    }

}