简单计算器的java实现

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

/**
*
* @author superzhao
*/
public class Calculate
{
public static void main(String[]args)
{
EventQueue.invokeLater(new Runnable()
{
public void run()
{
CalculatorFrame frame = new CalculatorFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(200,200);
frame.setResizable(false);
frame.setVisible(true);
}
});
}
}
class CalculatorFrame extends JFrame
{

public CalculatorFrame()
{
setTitle("简单计算器");
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;

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);
}

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);
}
}

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;
}
}
}
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);
}
}