计算器(JAVA)

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

public class Test7 {

public static void main(String[] args) {
CalculatorFrame frame=new CalculatorFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setBounds(100,100,200,200);
frame.setVisible(true);
}
}
class CalculatorFrame extends JFrame{
public CalculatorFrame(){
setTitle("计算器");
Container contentPane=getContentPane();
CalculatorPanel panel=new CalculatorPanel();
contentPane.add(panel);
}
}
class CalculatorPanel extends JPanel{
CalculatorPanel(){
setLayout(new BorderLayout());

result=0.0;
lastCommand="=";
start=true;
display=new TextField();

display.setEditable(false);

this.add(display,BorderLayout.NORTH);

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

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

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

add(panel,BorderLayout.CENTER);

}
public String getText(){
return display.getText();
}

public void append(String s){
String str=display.getText();
display.setText(str+s);
}

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

double result;
String lastCommand;
boolean start;
TextField display;
JPanel panel;

class InsertAction implements ActionListener{
public void actionPerformed(ActionEvent event){
String input=event.getActionCommand();
if(start){
display.setText("");
start=false;
}
display.setText(display.getText()+input);
}
}
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);
}
}