本题中，窗口的背景色为系统桌面的颜色，在窗口中分别画空心和实心的黑色矩形、深灰色圆角矩形和浅灰色椭圆形，并且画白色粗体的“欢迎学习Java!”字符串。
import java.awt.*;
import javax.swing.*;
public class java2

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("java2");
setSize(WIDTH,HEIGHT);
FillPanel panel=new FillPanel();
panel.setBackround(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);