本程序中，窗口的背景色为系统桌面的颜色，在窗口中分别画了空心和实心的黑色矩形、深灰色圆角矩形和浅灰色椭圆形，并且画了白色粗体的“欢迎学习Java!”字符串。

import java.awt.*;
import javax.swing.*;
public class exam_30
{
public static void main(String[] args)
{
FillFrame frame=new FillFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.show();
}
}
class FillFrame extends JFrame
{
public FillFrame()
{
setTitle("exam_30");
setSize(WIDTH, HEIGHT);
FillPanel panel=new FillPanel();
panel.setBackground(SystemColor.desktop);
Container contentPane=getContentPane();
contentPane.add(panel);
}
public static final int WIDTH=400;
public static final int HEIGHT=250;
}
class FillPanel extends JPanel
{
public void paintComponent(Graphics g)
{
______;
g setColor(new Color(10, 10, 10));
g drawRect(10, 10, 100, 30);
g setColor(new Color(100, 100, 100));
g drawRoundRect(150, 10, 100, 30, 15, 15);
g setColor(new Color(150, 150, 150));
g drawOval(280, 10, 80, 30);
g setColor(new Color(10, 10, 10));
g.fillRect(10, 110, 100, 30);
g.setColor(new Color(100, 100, 100));
g.fillRoundRect(150, 110, 100, 30, 15, 15);
g.setColor(new Color(150, 150, 150));
g.fillOval(280, 110, 80, 30);
g.setColor(Color.white);
Font f=new Font("宋体",______, 20);
g.setFont(f);
g.drawString("欢迎学习Java!", 150, 200);
}
}