用Java编写一个简单的计算器程序

import java.awt.*;
import java.awt.event.*;

public class CalcAppDemo extends Frame{
private TextField t_result;
private Panel p_main; //主面板
private Panel p_num; //数字面板
private Panel p_oper; //操作符面板
private Panel p_show; //显示面板
private Button b_num[]; //数字按钮
private Button b_oper[]; //操作符面板

public CalcAppDemo(String title){
setTitle(title);
t_result = new TextField("0.0", 21);
p_main = new Panel();
p_num = new Panel();
p_oper = new Panel();
p_show = new Panel();
p_main.setLayout(new BorderLayout());
p_num.setLayout(new GridLayout(4, 3, 1, 1));
p_oper.setLayout(new GridLayout(4, 2, 1, 1));

b_num = new Button[12];
for(int i=0; i<9; i++)
{
b_num[i] = new Button(new Integer(i+1).toString());
}
b_num[9] = new Button("0");
b_num[10] = new Button("cls");
b_num[11] = new Button(".");
for(int i=0; i<12; i++)
{
p_num.add(b_num[i]);
}

b_oper = new Button[8];
b_oper[0] = new Button("+");
b_oper[1] = new Button("-");
b_oper[2] = new Button("*");
b_oper[3] = new Button("/");
b_oper[4] = new Button("pow");
b_oper[5] = new Button("sqrt");
b_oper[6] = new Button("+/-");
b_oper[7] = new Button("=");
for(int i=0; i<8; i++) //
{
p_oper.add(b_oper[i]);
}

t_result.setEditable(false);
p_show.add(t_result, BorderLayout.NORTH);
p_main.add(p_show, BorderLayout.NORTH);
p_main.add(p_num, BorderLayout.WEST);
p_main.add(p_oper, BorderLayout.EAST);
this.add(p_main, BorderLayout.CENTER);
setSize(400, 400);
setResizable(false);
pack();

this.addWindowListener(new WindowAdapter(){
public void windowClosing(WindowEvent e)
{
System.exit(0);
}
});
ButtonListener b1 = new ButtonListener();
for(int i=0; i<12; i++)
{
b_num[i].addActionListener(b1);
}
for(int i=0; i<8; i++)
{
b_oper[i].addActionListener(b1);
}
}

class ButtonListener implements ActionListener
{
private String lastOp; //存储上一此操作符
private String strVal; //存储数字对应的字符串
private double total; //总数
private double number; //存储新输入的数
private boolean firsttime; //判断是否第一次按下的是操作符按钮
private boolean operatorPressed;//判断是否已经按过操作符按钮

ButtonListener()
{
firsttime = true;
strVal = "";
}

//事件处理器
public void actionPerformed(ActionEvent e)
{
String s = ((Button)e.getSource()).getLabel().trim();

if(Character.isDigit(s.charAt(0)))
{//判断是操作数还是操作符
handleNumber(s);
}
else
{
calculate(s);
}
}

//判断是一元操作符还是二元操作符，并根据操作符类型做计算
void calculate(String op)
{
operatorPressed = true;

if(firsttime&&! isUnary(op))
{
total = getNumberOnDisplay();
firsttime = false;
}
if(isUnary(op))
{
handleUnaryOp(op);
}
else if(lastOp != null)
{
handleBinaryOp(lastOp);
}
if(! isUnary(op))
{
lastOp = op;
}
}

//判断是否一元操作符
boolean isUnary(String s)
{
return s.equals("=")
||s.equals("cls")||s.equals("sqrt")
||s.equals("+/-")||s.equals(".");
}

//处理一元操作符
void handleUnaryOp(String op)
{
if(op.equals("+/-"))
{//
number = negate(getNumberOnDisplay() + "");
t_result.setText("");
t_result.setText(number + "");
return;
}else if(op.equals("."))
{
handleDecPoint();
return;
}else if(op.equals("sqrt"))
{
number = Math.sqrt(getNumberOnDisplay());
t_result.setText("");
t_result.setText(number + "");
return;
}else if(op.equals("="))
{//
if(lastOp!= null && !isUnary(lastOp))
{
handleBinaryOp(lastOp);
}
lastOp = null;
firsttime = true;
return;
}else
{
clear();
}
}

//处理二元运算符
void handleBinaryOp(String op)
{
if(op.equals("+"))
{
total +=number;
}else if(op.equals("-"))
{
total -=number;
}else if(op.equals("*"))
{
total *=number;
}else if(op.equals("/"))
{
try
{
total /=number;
}catch(ArithmeticException ae){}
}else if(op.equals("pow"))
total = Math.pow(total, number);
//t_result.setText("");
lastOp = null;
// strVal = "";
number = 0;
t_result.setText(total + "");
}

//该方法用于处理数字按钮
void handleNumber(String s)
{
if(!operatorPressed)
{
strVal += s;
}else
{
operatorPressed = false;
strVal = s;
}
//
number = new Double(strVal).doubleValue();
t_result.setText("");
t_result.setText(strVal);
}

//该方法用于按下"."按钮
void handleDecPoint()
{
operatorPressed = false;
//
if(strVal.indexOf(".")<0)
{
strVal += ".";
}
t_result.setText("");
t_result.setText(strVal);
}

//该方法用于将一个数求反
double negate(String s)
{
operatorPressed = false;
//如果是一个整数，去掉小数点后面的0
if(number == (int)number)
{
s = s.substring(0,s.indexOf("."));
}

//如果无"-"增加在该数的前面
if(s.indexOf("-")<0)
{
strVal = "-" + s;
}
else
{
strVal = s.substring(1);
}
return new Double(strVal).doubleValue();
}

//将显示框中的值转换成Double
double getNumberOnDisplay()
{
return new Double(t_result.getText()).doubleValue();
}

//清除屏幕并设置所有的标识
void clear()
{
firsttime = true;
lastOp = null;
strVal = "";
total = 0;
number = 0;
t_result.setText("0");
}
}

public static void main(String[] args) {
CalcAppDemo c = new CalcAppDemo("简单的计算器程序");
c.setVisible(true);
}

}