填空题 某小应用程序的界面有两个按钮，点击“画圆”按钮，程序在窗口画一个圆，点击“画矩形”按钮，程序在窗口画一个矩形。 import java.applet.*; import java.awt.*; import java.awt.event.*;import javax.swing.*; public class Class l extends Applet implements ActionListener { boolean c = false; int r = 50,a = 50, b = 50; JButton bl, b2; public void init1{ setSize(200, 200); setBackground(Color.blue); b1 = new JButton("画 圆"); b2 = new JButton("画矩形"); b1.addActionListener(this); b2.addActionListener(this); add(b1); add(b2); setVisible(true); } public void 2 (Graphics g){ g.clearRect(70, 100, 130, 200); g.setColor(Color. red); if(c) g.drawRoundRect(70, 100, r, r, r, r); else g.drawRect(70, 100, a, b); } public void update(Graphics g){ paint(g); } public void actionPerformed(ActionEvent e){ if(e.getSource3==b1) { c = true; } else if(e.getSource4==b2){ c = false; } 5； } }