這個是我再上一個的基礎上修改的，希望對大家有點幫助 
import javax.swing.*; 
//import javax.swing.event.*; 
import java.awt.*; 
import java.awt.event.*; 

//計算器顯示結果的窗體 
class Result extends JPanel { 
//text先是輸入和結果 
JTextField text = new JTextField("0"); 
Result() { 
//講輸入的數字或得到的結果在text的右邊顯示 
text.setHorizontalAlignment(SwingConstants.RIGHT); 
text.enable(false);//文本框不能編輯 
setLayout(new BorderLayout());//設定布局管理器邊框布局 
add(text, BorderLayout.CENTER);//text放置在窗體的中間 
} 
} 

//計算器數字按鈕定義面板 
class Number_Key extends JPanel { 
JButton zero = new JButton("0");//數字鍵0 
JButton one = new JButton("1");//數字鍵1 
JButton two = new JButton("2");//數字鍵2 
JButton three = new JButton("3");//數字鍵3 
JButton four = new JButton("4");//數字鍵4 
JButton five = new JButton("5");//數字鍵5 
JButton six = new JButton("6");//數字鍵6 
JButton seven = new JButton("7");//數字鍵7 
JButton eight = new JButton("8");//數字鍵8 
JButton nine = new JButton("9");//數字鍵9 
JButton plus = new JButton("+"); 
JButton sub = new JButton("-"); 
JButton mul = new JButton("*"); 
JButton div = new JButton("/"); 
JButton equal = new JButton("="); 
JButton ce = new JButton("ce");//置零鍵 
JButton point = new JButton("."); 
JButton tzero = new JButton("00"); 
Number_Key() { 
setLayout(new GridLayout(6, 3, 10, 10));//定義布局管理器為網格布局 
//添加各個按鈕鍵 
add(seven); 
add(eight); 
add(nine); 
add(four); 
add(five); 
add(six); 
add(one); 
add(two); 
add(three); 
add(zero); 
add(tzero); 
add(plus); 
add(sub); 
add(mul); 
add(div); 
add(point); 
add(equal); 
add(ce); 

} 
} 

//計算器主類 
public class Calculator extends JFrame implements ActionListener { 
Result result = new Result();//定義text的面板 
Number_Key number_key = new Number_Key();//定義按鈕面板 
//當點擊按鈕+、-、*、/時，com = true 
boolean com = false; 
//當i=0時說明是我們第一次輸入，字符串sum不會累加 
int i = 0; 
//存放text的內容 
String sum = ""; 
//存放點擊按鈕+、-、*、/之前的數值 
double total = 0; 
//+、-、*、/的代號分別為1，2，3，4 
int symbol = 0; 
Calculator() { 
super("Calculator");//設定標題 
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//設定關閉窗體時退出程序 
JPanel pane = new JPanel();//定義主面板 
pane.setLayout(new BorderLayout()); 
pane.add(result, BorderLayout.NORTH); 
pane.add(number_key, BorderLayout.SOUTH); 
number_key.one.addActionListener(this);//對1按鈕添加監聽事件 
number_key.two.addActionListener(this);//對2按鈕添加監聽事件 
number_key.three.addActionListener(this);//對3按鈕添加監聽事件 
number_key.four.addActionListener(this);//對4按鈕添加監聽事件 
number_key.five.addActionListener(this);//對5按鈕添加監聽事件 
number_key.six.addActionListener(this);//對6按鈕添加監聽事件 
number_key.seven.addActionListener(this);//對7按鈕添加監聽事件 
number_key.eight.addActionListener(this);//對8按鈕添加監聽事件 
number_key.nine.addActionListener(this);//對9按鈕添加監聽事件 
number_key.zero.addActionListener(this);//對0按鈕添加監聽事件 
number_key.ce.addActionListener(this);//對置零按鈕添加監聽事件 
number_key.plus.addActionListener(this);//對+按鈕添加監聽事件 
number_key.equal.addActionListener(this);//對=按鈕添加監聽事件 
number_key.sub.addActionListener(this);//對-按鈕添加監聽事件 
number_key.mul.addActionListener(this);//對*按鈕添加監聽事件 
number_key.div.addActionListener(this);//對/按鈕添加監聽事件 
number_key.tzero.addActionListener(this);//對00按鈕添加監聽事件 
number_key.point.addActionListener(this);//對.按鈕添加監聽事件 
setContentPane(pane); 
pack();//初始化窗體大小為正好盛放所有按鈕 
} 
//各個按鈕觸發的事件 
public void actionPerformed(ActionEvent e) { 
/*如果是點擊數字按鈕那么先要判斷是否在此之前點擊了+、-、*、/、=，如果是那么com=true 
* 如果沒有com= false;或者是否點擊數字鍵，如果是i = 1,如果沒有 i = 0; 
**/ 
if (e.getSource() == number_key.one) { 
if (com || i == 0) { 
result.text.setText("1"); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
result.text.setText(sum + "1"); 
} 
} else if (e.getSource() == number_key.two) { 
if (com || i == 0) { 
result.text.setText("2"); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
result.text.setText(sum + "2"); 
} 

} else if (e.getSource() == number_key.three) { 
if (com || i == 0) { 
result.text.setText("3"); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
result.text.setText(sum + "3"); 
} 
} else if (e.getSource() == number_key.four) { 
if (com || i == 0) { 
result.text.setText("4"); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
result.text.setText(sum + "4"); 
} 
} else if (e.getSource() == number_key.five) { 
if (com || i == 0) { 
result.text.setText("5"); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
result.text.setText(sum + "5"); 
} 
} else if (e.getSource() == number_key.six) { 
if (com || i == 0) { 
result.text.setText("6"); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
result.text.setText(sum + "6"); 
} 
} else if (e.getSource() == number_key.seven) { 
if (com || i == 0) { 
result.text.setText("7"); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
result.text.setText(sum + "7"); 
} 
} else if (e.getSource() == number_key.eight) { 
if (com || i == 0) { 
result.text.setText("8"); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
result.text.setText(sum + "8"); 
} 
} else if (e.getSource() == number_key.nine) { 
if (com || i == 0) { 
result.text.setText("9"); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
result.text.setText(sum + "9"); 
} 
} 
/*對于0這個按鈕有一定的說法，在我的程序里不會出現如00000這樣的情況，我加了判斷條件就是 
* 如果text中的數值=0就要判斷在這個數值中是否有.存在?如果有那么就在原來數值基礎之上添 
* 加0;否則保持原來的數值不變 
*/ 
else if (e.getSource() == number_key.zero) { 
if (com || i == 0) { 
result.text.setText("0"); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
if (Float.parseFloat(sum) > 0 || Float.parseFloat(sum) < 0) { 
result.text.setText(sum + "0"); 
} else { 
if (sum.trim().indexOf(".") == -1) { 
result.text.setText(sum); 
} else { 
result.text.setText(sum + "0"); 
} 
} 
} 
} else if (e.getSource() == number_key.ce) { 
result.text.setText("0"); 
i = 0; 
com = true; 
} else if (e.getSource() == number_key.tzero) { 
if (com || i == 0) { 
result.text.setText("0"); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
if (Float.parseFloat(sum) > 0 || Float.parseFloat(sum) < 0) { 
result.text.setText(sum + "00"); 
} else { 
if (sum.trim().indexOf(".") == -1) { 
result.text.setText(sum); 
} else { 
result.text.setText(sum + "00"); 
} 
} 
} 
} 
/*本程序不會讓一個數值中出現2個以上的小數點.具體做法是:判斷是否已經存在.存在就不添加, 
* 不存在就添加. 
*/ 
else if (e.getSource() == number_key.point) { 
if (com || i == 0) { 
result.text.setText("0."); 
com = false; 
i = 1; 
} else { 
sum = result.text.getText(); 
if (sum.trim().indexOf(".") == -1) { 
result.text.setText(sum + "."); 
} else { 
result.text.setText(sum); 
} 

} 
}//獲得點擊+之前的數值 
else if (e.getSource() == number_key.plus) { 
com = true; 
i = 0; 
total = Double.parseDouble(result.text.getText()); 
symbol = 1; 
}//獲得點擊-之前的數值 
else if (e.getSource() == number_key.sub) { 
com = true; 
i = 0; 
total = Double.parseDouble(result.text.getText()); 

symbol = 2; 
}//獲得點擊*之前的數值 
else if (e.getSource() == number_key.mul) { 
com = true; 
i = 0; 
total = Double.parseDouble(result.text.getText()); 
System.out.println(total); 
symbol = 3; 
}//獲得點擊/之前的數值 
else if (e.getSource() == number_key.div) { 
com = true; 
i = 0; 
total = Double.parseDouble(result.text.getText()); 
symbol = 4; 
} else if (e.getSource() == number_key.equal) { 
switch (symbol) { 
case 1 ://計算加法 
{ 
double ad = 
total + Double.parseDouble(result.text.getText()); 
result.text.setText(ad + ""); 
i = 0; 
sum = ""; 
break; 
} 
case 2 ://計算減法 
{ 
double ad = 
total - Double.parseDouble(result.text.getText()); 
result.text.setText(String.valueOf(ad)); 
i = 0; 
sum = ""; 
break; 
} 
case 3 ://計算乘法 
{ 
double ad = 
total * Double.parseDouble(result.text.getText()); 

result.text.setText(ad + ""); 
i = 0; 
sum = ""; 
break; 
} 
case 4 ://計算除法 
{ 
double ad = 
total / Double.parseDouble(result.text.getText()); 
result.text.setText(ad + ""); 
i = 0; 
sum = ""; 
break; 
} 
} 
System.out.println(com); 
} 
} 
public static void main(String[] args) { 
Calculator ww = new Calculator(); 
ww.show(); 
} 
}