小菜鸟请教计算器问题

Question

小弟初学Java核心技术，这个计算器有点看不懂。请各位高手帮忙写下监听器注释。如果要清零该怎样添加监听器。谢谢。
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);
}

}
);
}}
class CalculatorFrame extends JFrame
{
public CalculatorFrame()
{
setTitle("Calculator");
CalculatorPanel panel=new CalculatorPanel();
add(panel);
pack();
}
}
class CalculatorPanel extends JPanel
{
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(5,4));
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;
display.setText(""+result);
}
private JButton display;
private JPanel panel;
private double result;
private String lastCommand;
private boolean start;
}

Answer 1

/** 你程序本有错,清除功能加入下面就行了
*/
class CalculatorPanel extends JPanel {    public CalculatorPanel() {
    /////*********        JButton c = new JButton("C");
        c.addActionListener(new ActionListener() {            public void actionPerformed(ActionEvent e) {
                result=0;
                display.setText("0.0");
            }
        });
        add(c,BorderLayout.SOUTH);
    }