【考题】
  1、编写一个小型计算器应用程序，用户可从键盘输入两个整型变量，并可通过JComboBox选择计算操作符，计算结果在JtextField中显示，界面风格请参照Windows计算器界面。 

【01】
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public class Calculator extends JFrame implements ActionListener,ItemListener {
 JTextField jtf1=new JTextField("0",10);
 JTextField jtf2=new JTextField("0",10);
 JTextField jtf3=new JTextField(10);
 JLabel jla=new JLabel("=");
 JComboBox jcb=new JComboBox();
 JButton jb=new JButton("重置数字");
    public Calculator() {
     JPanel jPanel=(JPanel)this.getContentPane();
     jPanel.setLayout(new BorderLayout());    
     JPanel jPanel01=new JPanel();
     JPanel jPanel02=new JPanel();
     jPanel.add(jPanel01,"North");
     jPanel.add(jPanel02,"South");
      
     jcb.addItem(" ");     
     jcb.addItem("+");
     jcb.addItem("-");
     jcb.addItem("*");
     jcb.addItem("/");
     
     jPanel01.add(jtf1);