java实现简易计算器

package com.phoenix;

import java.awt.BorderLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;

@SuppressWarnings("serial")
public class CaculatorPanel extends JPanel{
private JButton display;
private JPanel panel;
private double result;
private String lastCommand;
private boolean start;

public CaculatorPanel() {
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();

// add the buttons in a 4 * 4 grid
panel = new JPanel();
panel.setLayout(new GridLayout(4, 4));

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

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

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

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

add(panel, BorderLayout.CENTER);

}

private void addButtons(String lable, ActionListener listener) {
JButton button = new JButton(lable);
button.addActionListener(listener);
panel.add(button);
}

private class InsertAction implements ActionListener {

@Override
public void actionPerformed(ActionEvent e) {
String input = e.getActionCommand();
if (start) {
display.setText("");
start = false;
}
display.setText(display.getText() + input);
}
}

private class CommandAction implements ActionListener {

@Override
public void actionPerformed(ActionEvent e) {
String command = e.getActionCommand();

if (start) {
if (command.equals("-")) {
display.setText(command);
start = false;
}else {
lastCommand = command;
}
}else {
caculate(Double.parseDouble(display.getText()));
lastCommand = command;
start = true;
}
}
}

public void caculate(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);
}
}