今天老师让做一个计算器，简单的布局自己可以完成，但是里面的判断代码不会 ，就去百度了一下，自己也把不懂的地方搞懂之后加了注释，分享给大家
import java.awt.*;
import javax.swing.*;
/**
* A simple calculator program.
* <p>I saw this program in a QQ group, and help a friend correct it.</p>
*
* @author Singyuen Yip
* @version 1.00 12/29/2009
* @see JFrame
* @see ActionListener
*/
public class JCalculator extends JFrame implements ActionListener {
/**
* SerialVersionUID Java的序列化机制
*/
private static final long serialVersionUID = -169068472193786457L;
/**
* This class help close the Window.
* @author Singyuen Yip
*
*/
private class WindowCloser extends WindowAdapter {
public void windowClosing(WindowEvent we) {
System.exit(0);
}
}
int i;
// Strings for Digit & Operator buttons. 数字 和操作按钮
private final String[] str = { "7", "8", "9", "/", "4", "5", "6", "*", "1",
"2", "3", "-", ".", "0", "=", "+" };
// Build buttons.按钮数组
JButton[] buttons = new JButton[str.length];
// For cancel or reset. 取消 或者 重置清零按钮
JButton reset = new JButton("CE");
// Build the text field to show the result. 文本框display
JTextField display = new JTextField("0");
/**
* Constructor without parameters.构造函数没有参数
*/
public JCalculator() {
super("Calculator");
// Add a panel. 画板1
JPanel panel1 = new JPanel(new GridLayout(4, 4));
// panel1.setLayout(new GridLayout(4,4));画板1上网格布局
//将按钮添加到画板1上
for (i = 0; i < str.length; i++) {
buttons[i] = new JButton(str[i]);
panel1.add(buttons[i]);
}
//画板2 边界布局
JPanel panel2 = new JPanel(new BorderLayout());
// panel2.setLayout(new BorderLayout());
//画板2上添加文本框display 按钮reset
panel2.add("Center", display);
panel2.add("East", reset);
// JPanel panel3 = new Panel(); 画板3
/*获取内容面板，因为JFrame不能直接添加组件，
* 需要用getContentPane()函数获取内容面板，
* 再在内容面板上进行添加组件*/
getContentPane().setLayout(new BorderLayout());
getContentPane().add("North", panel2);
getContentPane().add("Center", panel1);
// Add action listener for each digit & operator button.
for (i = 0; i < str.length; i++)
buttons[i].addActionListener(this);
// Add listener for "reset" button.
reset.addActionListener(this);
// Add listener for "display" button.
display.addActionListener(this);
// The "close" button "X".
addWindowListener(new WindowCloser());
// Initialize the window size.
setSize(800, 800);
// Show the window.
// show(); Using show() while JDK version is below 1.5.
setVisible(true);
// Fit the certain size.适合一定的大小
/*关于pack（）方法
在 Frame 类中有一个从类 java.awt.Window 继承的方法 pack()
show() 同样也继承自 java.awt.Window
public void pack()
调整此窗口的大小，以适合其子组件的首选大小和布局。
如果该窗口和/或其所有者仍不可显示，则两者在计算首
选大小之前变得可显示。在计算首选大小之后，将会验证
该 Window*/
pack();
}
public void actionPerformed(ActionEvent e) {
Object target = e.getSource();//target=输入的object
String label = e.getActionCommand();//返回与此动作相关的命令字符串。
if (target == reset)
handleReset();//后面有handleaReset方法的定义
else if ("0123456789.".indexOf(label) > 0)
handleNumber(label);//后面有handleaNumber方法的定义
else
handleOperator(label);//后面有handleaOperator方法的定义
}
// Is the first digit pressed?
boolean isFirstDigit = true;
/**
* Number handling.
* @param key the key of the button.
*/
public void handleNumber(String key) {
if (isFirstDigit)
display.setText(key);
else if ((key.equals(".")) && (display.getText().indexOf(".") < 0))
display.setText(display.getText() + ".");
else if (!key.equals("."))
display.setText(display.getText() + key);
isFirstDigit = false;
}
/**
* Reset the calculator.
*/
public void handleReset() {
display.setText("0");
isFirstDigit = true;
operator = "=";
}
double number = 0.0;
String operator = "=";
/**
* Handling the operation.
* @param key pressed operator's key.
*/
public void handleOperator(String key) {
if (operator.equals("+"))
number += Double.valueOf(display.getText());
else if (operator.equals("-"))
number -= Double.valueOf(display.getText());
else if (operator.equals("*"))
number *= Double.valueOf(display.getText());
else if (operator.equals("/"))
number /= Double.valueOf(display.getText());
else if (operator.equals("="))
number = Double.valueOf(display.getText());
display.setText(String.valueOf(number));
operator = key;
isFirstDigit = true;
}
public static void main(String[] args) {
new JCalculator();
}
}