calculator.java

Java程序设计技巧与开发实例附书源代码。

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

public class Calculator
    extends Applet
    implements ActionListener
{ //在这里定义用于GUI组件的私有成员变量和其它的用于applet内部任务的成员变量
   private final String[] KEYS =
       {
       "7", "8", "9", "/",
       "4", "5", "6", "*",
       "1", "2", "3", "-",
       ".", "0", "=", "+"};
   private Button keys[] = new Button[KEYS.length];
   private Button reset = new Button(" CE ");
   private TextField display = new TextField("0");
   private boolean firstDigit = true;
   private double number = 0.0;
   private String operator = "=";

   private void setup()
   {
      Panel calcKeys = new Panel();
      calcKeys.setLayout(new GridLayout(4, 4));
      for (int i = 0; i < KEYS.length; i++)
      {
         keys[i] = new Button(KEYS[i]);
         calcKeys.add(keys[i]);
      }
      Panel top = new Panel();
      top.setLayout(new BorderLayout());
      top.add("Center", display);
      top.add("East", reset);

      setLayout(new BorderLayout());
      add("North", top);
      add("Center", calcKeys);
   }

   public void init()
   {
      setup();
      for (int i = 0; i < KEYS.length; i++)
      {
         keys[i].addActionListener(this);
      }
      reset.addActionListener(this);
      display.setEditable(false);
   }

   //添加需要的动作处理方法
   public void actionPerformed(ActionEvent e)
   {
      Object target = e.getSource();
      String label = e.getActionCommand();
      if (target == reset)
      {
         handleReset();
      }
      else if ("0123456789.".indexOf(label) >= 0)
      {
         handleNumber(label);
      }
      else
      {
         handleOperator(label);
      }
   }

   private void handleNumber(String key)
   {
      if (firstDigit)
      {
         display.setText(key);
      }
      else if ( (key.equals(".")) && (display.getText().indexOf(".") < 0))
      {
         display.setText(display.getText() + ".");
      }
      else if (!key.equals("."))
      {
         display.setText(display.getText() + key);
      }
      firstDigit = false;
   }

   private void handleOperator(String key)
   {
      if (operator.equals("+"))
      {
         number += getNumberFromDisplay();
      }
      else if (operator.equals("-"))
      {
         number -= getNumberFromDisplay();
      }
      else if (operator.equals("*"))
      {
         number *= getNumberFromDisplay();
      }
      else if (operator.equals("/"))
      {
         number /= getNumberFromDisplay();
      }
      else if (operator.equals("="))
      {
         number = getNumberFromDisplay();
      }
      display.setText(String.valueOf(number));
      operator = key;
      firstDigit = true;
   }

   private double getNumberFromDisplay()
   {
      return Double.valueOf(display.getText()).doubleValue();
   }

   private void handleReset()
   {
      display.setText("0");
      firstDigit = true;
      operator = "=";
   }
}