主类代码如下

package jpanel;

import java.awt.EventQueue;

import javax.swing.JFrame;

public class ColorPanel {

	private JFrame frame;

	/**
	 * Launch the application.
	 */
	public static void main(String[] args) {
		EventQueue.invokeLater(new Runnable() {
			public void run() {
				try {
					ColorPanel window = new ColorPanel();
					window.frame.setVisible(true);
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		});
	}

	/**
	 * Create the application.
	 */
	public ColorPanel() {
		initialize();
	}

	/**
	 * Initialize the contents of the frame.
	 */
	private void initialize() {
		frame = new JFrame();
		frame.setBounds(100, 100, 450, 300);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.getContentPane().setLayout(null);
		
		ShadePanel sPanel=new ShadePanel();
		
		sPanel.setBounds(0,0,432,253);
		
		frame.getContentPane().add(sPanel);
	}
}

重写的JPanel类代码如下

package jpanel;


import java.awt.Color;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JPanel;

/**
 * 带背景的面板组件
 */
public class ShadePanel extends JPanel {
    /**
     * 构造方法
     */
    public ShadePanel() {
        super();
        setLayout(null);
    }
    
    @Override
    protected void paintComponent(Graphics g1) {// 重写绘制组件外观
        Graphics2D g = (Graphics2D) g1;
        super.paintComponent(g);// 执行超类方法
        int width = getWidth();// 获取组件大小
        int height = getHeight();
        // 创建填充模式对象
        GradientPaint paint = new GradientPaint(0, 0, Color.CYAN, 0, height,
                Color.MAGENTA);
        g.setPaint(paint);// 设置绘图对象的填充模式
        g.fillRect(0, 0, width, height);// 绘制矩形填充控件界面
    }
}