java 简单的计算器程序实例代码

java 简单的计算器程序

实现实例：

import java.awt.*;
import java.awt.event.*;
import javax.swing.*; 

public class Calculator
{
  public static void main(String[] args)
  {
   EventQueue.invokeLater(new Runnable()
     {
      public void run()
      {
        CalculatorFrame frame = new CalculatorFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
      }
     });
  }
} 

/**
 * A frame with a calculator panel.
 */
class CalculatorFrame extends JFrame
{
  public CalculatorFrame()
  {
    setTitle("Calculator");
    CalculatorPanel panel=new CalculatorPanel();
    add(panel);
    pack();
  }
} 

class CalculatorPanel extends JPanel
{
  private JButton display;
    private JPanel panel;
    private double result;
    private String lastCommand;
    private boolean start;
  public CalculatorPanel()
  {
    setLayout(new BorderLayout()); 

    result=0;
    lastCommand="=";
    start=true; 

     // add the display
    display=new JButton("0");
    display.setEnabled(false);
    add(display,BorderLayout.NORTH); 

    ActionListener insert=new InsertAction();
    ActionListener command=new CommandAction(); 

    panel=new JPanel();
    panel.setLayout(new GridLayout(4,4)); 

     addButton("7", insert);
     addButton("8", insert);
     addButton("9", insert);
     addButton("/", command); 

     addButton("4", insert);
     addButton("5", insert);
     addButton("6", insert);
     addButton("*", command); 

     addButton("1", insert);
     addButton("2", insert);
     addButton("3", insert);
     addButton("-", command); 

     addButton("0", insert);
     addButton(".", insert);
     addButton("=", command);
     addButton("+", command); 

     add(panel, BorderLayout.CENTER); 

    }
  private void addButton(String label,ActionListener listener)
  {
    JButton button=new JButton(label);
    button.addActionListener(listener);
    panel.add(button);
  }
  /**
    * This action inserts the button action string to the end of the display text.
    */
  private class InsertAction implements ActionListener
  {
    public void actionPerformed(ActionEvent event)
    {
      String input=event.getActionCommand();
      if(start)
      {
        display.setText("");
        start=false;
      }
      display.setText(display.getText()+input);
    }
  }
   /**
    * This action executes the command that the button action string denotes.
    */
  private class CommandAction implements ActionListener
  {
    public void actionPerformed(ActionEvent event)
    {
      String command=event.getActionCommand();
      if(start)
      {
        if (command.equals("-"))
        {
          display.setText(command);
          start = false;
        }
        else lastCommand = command;
      }else {
        calculate(Double.parseDouble(display.getText()));
        lastCommand=command;
        start=true;
      }
    }
  }
  /**
    * Carries out the pending calculation.
    * @param x the value to be accumulated with the prior result.
    */
  public void calculate(double x)
  {
     if (lastCommand.equals("+")) result += x;
     else if (lastCommand.equals("-")) result -= x;
     else if (lastCommand.equals("*")) result *= x;
     else if (lastCommand.equals("/")) result /= x;
     else if (lastCommand.equals("=")) result = x;
     display.setText("" + result);
  }
}

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