java计算器

//计算器
// Calculator.java
public class Calculator {

  private static final char NO_OP = '\0';
  private static final char PLUS = '+';
  private static final char SUBTRACT = '-';
  private static final char MULTIPLY = '*';
  private static final char DIVIDE = '/';

  private float  number1 = 0.0F;
  //private float  number2 = Float.NaN;
  private char   operator = NO_OP;

  //等于运算
  public String opEquals(String number) {
    float result;

    if ( operator == NO_OP ) {
      result = parseNumber(number);
    } else {
      result = performOperation(parseNumber(number));
    }
    operator = NO_OP;

    number1 = result;

    return Float.toString(result);
  }

  //加法运算
  public String opAdd(String number) {
    float result;

    if ( operator == NO_OP ) {
      result = parseNumber(number);
    } else {
      result = performOperation(parseNumber(number));
    }
    operator = PLUS;

    number1 = result;

    return Float.toString(result);
  }

  //减法运算
  public String opSubtract(String number) {
    float result;

    if ( operator == NO_OP ) {
      result = parseNumber(number);
    } else {
      result = performOperation(parseNumber(number));
    }
    operator = SUBTRACT;

    number1 = result;

    return Float.toString(result);
  }

  //乘法运算
  public String opMultiply(String number) {
    float result;

    if ( operator == NO_OP ) {
      result = parseNumber(number);
    } else {
      result = performOperation(parseNumber(number));
    }
    operator = MULTIPLY;

    number1 = result;

    return Float.toString(result);
  }

  //除法运算
  public String opDivide(String number) {
    float result;

    if ( operator == NO_OP ) {
      result = parseNumber(number);
    } else {
      result = performOperation(parseNumber(number));
    }
    operator = DIVIDE;

    number1 = result;

    return Float.toString(result);
  }

  //处理运算符
  private float performOperation(float number2) {
    float result = 0.0F;

    switch ( operator ) {
    case PLUS:
      result = number1 + number2;
      break;
    case SUBTRACT:
      result = number1 - number2;
      break;
    case MULTIPLY:
      result = number1 * number2;
      break;
    case DIVIDE:
      result = number1 / number2;
      break;
    }

    return result;
  }

  //将字符串类型转换为浮点型
  private static float parseNumber(String number) {
    float real_number;

    try {
      real_number = Float.parseFloat(number);
    } catch (NumberFormatException e) {
      real_number = Float.NaN;
    }

    return real_number;
  }

}


// CalculatorGUI.java
import java.awt.*;
import java.awt.event.*;

public class CalculatorGUI {

  // 定义按钮
  private Button key0, key1, key2, key3, key4;
  private Button key5, key6, key7, key8, key9;
  private Button keyequal, keyplus, keyminus;
  private Button keyperiod, keymult, keydiv;
 
  // 定义存放按钮的区域
  private Panel buttonArea;
 
  // 定义存放运算结果的区域
  private Label answer;
 
  // 用来实现运算功能的类的对象实例化
  private Calculator calculator;
  private boolean    readyForNextNumber;

  public CalculatorGUI() {
    calculator = new Calculator();
    readyForNextNumber = true;

    answer = new Label("0.0",Label.RIGHT);

    key0 = new Button("0");
    key1 = new Button("1");
    key2 = new Button("2");
    key3 = new Button("3");
    key4 = new Button("4");
    key5 = new Button("5");
    key6 = new Button("6");
    key7 = new Button("7");
    key8 = new Button("8");
    key9 = new Button("9");
    keyequal = new Button("=");
    keyplus = new Button("+");
    keyminus = new Button("-");
    keymult = new Button("*");
    keydiv = new Button("/");
    keyperiod = new Button(".");
    buttonArea = new Panel();
  }

  public void launchFrame() {
    buttonArea.setLayout(new GridLayout(4,4));

    buttonArea.add(key7);
    buttonArea.add(key8);
    buttonArea.add(key9);
    buttonArea.add(keyplus);
    buttonArea.add(key4);
    buttonArea.add(key5);
    buttonArea.add(key6);
    buttonArea.add(keyminus);
    buttonArea.add(key1);
    buttonArea.add(key2);
    buttonArea.add(key3);
    buttonArea.add(keymult);
    buttonArea.add(key0);
    buttonArea.add(keyperiod);
    buttonArea.add(keyequal);
    buttonArea.add(keydiv);

    // 设置事件接收句柄
    OpButtonHanlder op_handler = new OpButtonHanlder();
    NumberButtonHanlder number_handler = new NumberButtonHanlder();
    key0.addActionListener(number_handler);
    key1.addActionListener(number_handler);
    key2.addActionListener(number_handler);
    key3.addActionListener(number_handler);
    key4.addActionListener(number_handler);
    key5.addActionListener(number_handler);
    key6.addActionListener(number_handler);
    key7.addActionListener(number_handler);
    key8.addActionListener(number_handler);
    key9.addActionListener(number_handler);
    keyperiod.addActionListener(number_handler);
    keyplus.addActionListener(op_handler);
    keyminus.addActionListener(op_handler);
    keymult.addActionListener(op_handler);
    keydiv.addActionListener(op_handler);
    keyequal.addActionListener(op_handler);

    // 新建一个帧，并且加上消息监听
    Frame f = new Frame("Calculator");
    f.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
  System.exit(0);
}
    });
    f.setSize(200, 200);

    f.add(answer, BorderLayout.NORTH);
    f.add(buttonArea, BorderLayout.CENTER);
    f.setVisible (true);
  }

  //响应按钮事件，并根据不同的按钮事件进行不同的运算
  private class OpButtonHanlder implements ActionListener {
    public void actionPerformed(ActionEvent event) {
      char  operator = event.getActionCommand().charAt(0);
      String result = "";
      switch  ( operator ) {
      case '+':
result = calculator.opAdd(answer.getText());
break;
      case '-':
result = calculator.opSubtract(answer.getText());
break;
      case '*':
result = calculator.opMultiply(answer.getText());
break;
      case '/':
result = calculator.opDivide(answer.getText());
break;
      case '=':
result = calculator.opEquals(answer.getText());
break;
      }
      answer.setText(result);
      readyForNextNumber = true;
    }
  }

  //处理连续运算时主界面的显示
  private class NumberButtonHanlder implements ActionListener {
    public void actionPerformed(ActionEvent event) {
      if ( readyForNextNumber ) {
answer.setText(event.getActionCommand());
readyForNextNumber = false;
      } else {
answer.setText(answer.getText() + event.getActionCommand().charAt(0));
      }
    }
  }

//主函数，也是该应用程序的执行入口处
  public static void main(String args[]) {
    CalculatorGUI calcGUI = new CalculatorGUI();
    calcGUI.launchFrame();
  }
}