StingBuffer
import javax.swing.*;
package a;
import java.awt.event.*;
import java.awt.*;
public class Calculator1 extends Frame implements ActionListener {
Frame frame;
Panel panel;
TextField t;
Button[] button;
  StringBuffer str=new StringBuffer("");
  double x, y;
  int z;
  Calculator1()
  {
  frame=new Frame();
  frame.setLayout(new BorderLayout());
  MenuBar mb=new MenuBar();
  Menu menu1=new Menu("编辑(E)");
  Menu menu2=new Menu("查看(v)");
  Menu menu3=new Menu("帮助(H)");
  MenuItem mi1=new MenuItem("复制(C) Ctrl+C ");
  MenuItem mi2=new MenuItem("粘贴(V) Ctrl+V ");
  MenuItem m2=new MenuItem("退出");
  m2.addActionListener(new ActionListener(){
  public void actionPerformed(ActionEvent e2) 
  {  
  System.exit(0);
  } 
  });
  MenuItem mi3=new MenuItem("标准型(T) ");
  MenuItem mi4=new MenuItem("科学型(S) ");
  MenuItem mi5=new MenuItem("数据分组(I) ");
  MenuItem mi6=new MenuItem("帮助主题(H) ");
  MenuItem mi7=new MenuItem("关于计算器(A) ");
  String s[]={"My","love","退格","CE","C","7","8","9","+/-","sqrt","4","5","6","/","%","1","2","3","-","0","*","1/x",".","+","="};
  button=new Button[s.length];
  panel=new Panel();
  panel.setLayout(new GridLayout(5,5));
  t=new TextField("0",27);
  t.setEnabled(false); 
  for(int i=0;i<button.length;i++)
  {
  button[i]=new Button(s[i]);
  button[i].setForeground(Color.blue);
  panel.add(button[i]);
  }  
  for(int i=0;i<button.length;i++)
  {
  button[i].addActionListener(this);
  // button[i].setBackground(new Color(194,171,245));
  }
  button[0].addMouseListener(new MouseAdapter(){
  public void mouseEntered(MouseEvent e){
  button[0].setBackground(Color.cyan);
  }
  });
  button[0].addMouseListener(new MouseAdapter(){
  public void mouseExited(MouseEvent e){
  // button[0].setBackground());
  }});
  mb.add(menu1);
  mb.add(menu2);
  mb.add(menu3);
  mb.add(menu1);
  mb.add(menu2);
  mb.add(menu3);
  menu1.add(mi1);
  menu1.add(mi2);
  menu1.add(m2);
  menu2.add(mi3);
  menu2.add(mi4);
  menu2.add(mi5);
  menu3.add(mi6);
  menu3.add(mi7); 
  frame.setMenuBar(mb);
  frame.setBounds(300,300,260,370);
  frame.add(t,BorderLayout.NORTH);
  frame.add(panel,BorderLayout.CENTER);
  frame.setBackground(Color.blue);
  frame.setResizable(false);
  frame.setVisible(true);  
  frame.addWindowListener(new WindowAdapter(){