Java语言编写的计算器代码

Question

以下为Java语言编写的一段具有计算功能的计算器的代码

package JavaApplication2; 
import java.awt.*;
import java.awt.event.*;
//import javax.swing.*;
class CalculatorPanel extends Panel implements ActionListener
{
public CalculatorPanel(){
setLayout(new BorderLayout());
display = new TextField("0");
display.setEditable(false);
add(display, "North");
Panel p = new Panel();
p.setLayout(new GridLayout(4, 4));
String buttons = "789/456*123-0.=+";
for (int i = 0; i < buttons.length(); i++) 
addButton(p, buttons.substring(i, i + 1));
add(p, "Center");
}
private void addButton(Container c, String s){  
Button b = new Button(s);
c.add(b);
b.addActionListener(this);
}


public void actionPerformed(ActionEvent evt) {  
String s = evt.getActionCommand();
if ('0' <= s.charAt(0) && s.charAt(0) <= '9' 
|| s.equals(".")){
if (start) display.setText(s);
else display.setText(display.getText() + s);
start = false;
}
else{
if (start){ 
if (s.equals("-")) {
display.setText(s); start = false; 
}
else op = s;
}
else{
double x = Double.parseDouble(display.getText());
calculate(x);
op = s;
start = true;
}
}
}
public void calculate(double n) {
if (op.equals("+")) arg += n;
else if (op.equals("-")) arg -= n;
else if (op.equals("*")) arg *= n;
else if (op.equals("/")) arg /= n;
else if (op.equals("=")) arg = n;
display.setText("" + arg);
}


private TextField display;
private double arg = 0;
private String op = "=";
private boolean start = true;
}
class CalculatorFrame extends Frame { 
public CalculatorFrame() {  
setTitle("Calculator");
setSize(200, 200);
addWindowListener(new WindowAdapter(){  
public void windowClosing(WindowEvent e){ 
System.exit(0);
}
} );
//Container contentPane = getContentPane();
this.add(new CalculatorPanel());
}
}
public class MyAWTCalculator {
public static void main(String args[] ) { 
Frame frame = new CalculatorFrame();
frame.setVisible(true);
}
}


本人菜鸟一枚，正在自学Java。完全不懂这段代码，希望大神们帮助我通过这个实例弄懂一小部分Java语言。我想知道这里面的每一步都是干什么的，具体到哪实现了界面、计算...又都是怎么实现的？希望能有大神作为我的带路人，将我带上Java语言的道路。

Answer 1

哦哦，谢谢你啦，我会改进的

Answer 2

public void calculate(double n) {

if (op.equals("+")) arg += n;

else if (op.equals("-")) arg -= n;

else if (op.equals("*")) arg *= n;

else if (op.equals("/")) arg /= n;

else if (op.equals("=")) arg = n;

display.setText("" + arg);

}

这段代码直接使用+-*/进行计算，是存在精度问题的，建议使用BigDecimal的add、subtract、multiply、divide