本题程序的功能是计算圆和三角形的面积。通过菜单“选择”可以分别进行圆和三角形面积的计算。单击菜单项“圆面积计算”，窗口中就会显示两个文本框和一个“确定”按钮，在第一个文本框中输入圆的半径，单击“确定”按钮后就可以在第二个文本框中显示圆的面积。单击菜单项“三角形面积计算”，窗口中就会显示4个文本框和一个“确定”按钮，在前三个文本框中分别输入三角形三个边的长度，单击“确定”按钮后，如果三个边的长度不能组成三角形，结果文本框中会给出提示信息，否则显示三角形的面积；如果输入的值不是数值，则会给出提示信息。请将下述程序补充完整(注意：不得改动程序的结构，不得增行或删行)。
import java.awt.*;
import java.awt.event.*;
class circle extends Panel implements AetionListener
double r,area;
TextField radius = null,result = null;
Button b = null;
______;
radius = new TextField(10);
result = new TextField(10);
b = new Button("确定");
add (new Label ("输入半径"));
add (radius);
add(new Label("面积是"));
add(result);
add(b);
b.addActionListener (this);
result,setEnabled (false);
public void actionPerformed(ActionEvent e)
try
r = Double.parseDouble (radius.getText ());
area =Math.PI*r*r;
result,setText (""+area);
catch (Exception ee)
radius.setText ("请输入数字字符");
class triangle extends Panel implements ActionListener
double a = 0,b = 0,c = 0,area;
TextField border a = new TextField(6) ;
TextField border b = new TextField(6) ;
TextField border c = new TextField(6) ;
Result = new TextField(24);
Button button = new Button("确定");
triangle ()
add(new Label("输入三边的长度"));
add (border_a);
add (border_b);
add (border_c);
add(new Label("面积是:"));
add (result);
add (button);
button,addActionListener (this);
result.setEnabled(false);
public void actionPerformed(ActionEvent e)
try
a = Double.parseDoubleborder_a.getText());
b = Double.parseDouble(border_b.getText());
c = Double.parseDouble(border_c.getText());
if(a+b＞c＆＆a+c＞b＆＆c+b＞a)
double p = (a+b+c)/2;
area = Math.sqrt(p*(p-a)*(p-b)*(p-c));
result.setText(""+ area);
else
result.setText ("您输入的数字不能形成三角形");
catch(Exception ee)
result.setText ("请输入数字字符");
class Win ______ implements ActionListener
MenuBar bar = null;
Menu menu = null;
MenuItem item1,item2;
circle circle;
triangle trangle;
Win()
bar = new MenuBar(); menu = new Menu("选择");
setSize(300,200);
item1 = new MenuItem("圆面积计算");
item2 = new MenuItem("三角形面积计算");
menu.add(item1);
menu.add(item2);
bar.add(menu);
setMenuBar(bar);
circle = new circle();
trangle = new triangle();
item1.addActionListener(this);
item2.addActionListener(this);
setVisible(true);
public void actionPerformed(ActionEvent e)
if (e.getSource() == item1)
removeAll();
add(circle,"Center");
validate();
else
if(e.getSource() == item2)
removeAll ();
add (trangle,"Center");
validate ();
public class advance
public static void main (String args[])
Win win = new Win();
win.setTitle ("advance ");
win.setBounds (100,100,700,300);
win.setVisible (true);
win.addWindowListener (______)
public void windowClosing(WindowEvent e)
System.exit (0);
);
