calculator.java

这是《Java案例精粹150例（上册）》一书配套的源代码。

// Calculator.java

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

//计算器显示结果的窗体
class Result extends JPanel {
	//text先是输入和结果
	JTextField text = new JTextField("0");

	Result() {
		//讲输入的数字或得到的结果在text的右边显示
		text.setHorizontalAlignment(SwingConstants.RIGHT);
		text.enable(false);//文本框不能编辑
		setLayout(new BorderLayout());//设定布局管理器边框布局
		add(text, BorderLayout.CENTER);//text放置在窗体的中间
	}
}

//计算器数字按钮定义面板

class Number_Key extends JPanel {
	JButton zero = new JButton("0"); //数字键0

	JButton one = new JButton("1"); //数字键1

	JButton two = new JButton("2"); //数字键2

	JButton three = new JButton("3"); //数字键3

	JButton four = new JButton("4"); //数字键4

	JButton five = new JButton("5"); //数字键5

	JButton six = new JButton("6"); //数字键6

	JButton seven = new JButton("7"); //数字键7

	JButton eight = new JButton("8"); //数字键8

	JButton nine = new JButton("9"); // 数字键9

	JButton plus = new JButton("+");

	JButton sub = new JButton("-");

	JButton mul = new JButton("*");

	JButton div = new JButton("/");

	JButton equal = new JButton("=");

	JButton ce = new JButton("ce"); // 置零键

	JButton point = new JButton(".");

	JButton tzero = new JButton("00");

	Number_Key() {
		// 定义布局管理器为网格布局
		setLayout(new GridLayout(6, 3, 10, 10));
		// 添加各个按钮键
		add(seven);
		add(eight);
		add(nine);
		add(four);
		add(five);
		add(six);
		add(one);
		add(two);
		add(three);
		add(zero);
		add(tzero);
		add(plus);
		add(sub);
		add(mul);
		add(div);
		add(point);
		add(equal);
		add(ce);
	}
}

// 计算器主类

public class Calculator extends JFrame implements ActionListener {
	Result result = new Result(); // 定义text的面板

	Number_Key number_key = new Number_Key(); // 定义按钮面板

	//	当点击按钮+、-、*、/时，com = true
	boolean com = false;

	//	当i=0时说明是我们第一次输入，字符串sum不会累加
	int i = 0;

	//	存放text的内容
	String sum = "";

	//存放点击按钮+、-、*、/之前的数值
	double total = 0;

	//+、-、*、/的代号分别为1，2，3，4
	int symbol = 0;

	Calculator() {
		super("Calculator");//设定标题
		setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//设定关闭窗体时退出程序
		JPanel pane = new JPanel();//定义主面板
		pane.setLayout(new BorderLayout());
		pane.add(result, BorderLayout.NORTH);
		pane.add(number_key, BorderLayout.SOUTH);
		number_key.one.addActionListener(this);//对1按钮添加监听事件
		number_key.two.addActionListener(this);//对2按钮添加监听事件
		number_key.three.addActionListener(this);//对3按钮添加监听事件
		number_key.four.addActionListener(this);//对4按钮添加监听事件
		number_key.five.addActionListener(this);//对5按钮添加监听事件
		number_key.six.addActionListener(this);//对6按钮添加监听事件
		number_key.seven.addActionListener(this);//对7按钮添加监听事件
		number_key.eight.addActionListener(this);//对8按钮添加监听事件
		number_key.nine.addActionListener(this);//对9按钮添加监听事件
		number_key.zero.addActionListener(this);//对0按钮添加监听事件
		number_key.ce.addActionListener(this);//对置零按钮添加监听事件
		number_key.plus.addActionListener(this);//对+按钮添加监听事件
		number_key.equal.addActionListener(this);//对=按钮添加监听事件
		number_key.sub.addActionListener(this);//对-按钮添加监听事件
		number_key.mul.addActionListener(this);//对*按钮添加监听事件
		number_key.div.addActionListener(this);//对/按钮添加监听事件
		number_key.tzero.addActionListener(this);//对00按钮添加监听事件
		number_key.point.addActionListener(this);//对.按钮添加监听事件
		setContentPane(pane);
		pack();//初始化窗体大小为正好盛放所有按钮
	}

	//各个按钮触发的事件
	public void actionPerformed(ActionEvent e) {
		/*
		 * 如果是点击数字按钮那么先要判断是否在此之前点击了+、-、*、/、=，如果是那么com=true 如果没有com=
		 * false;或者是否点击数字键，如果是i = 1,如果没有 i = 0;
		 */
		if (e.getSource() == number_key.one) {
			if (com || i == 0) {
				result.text.setText("1");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				result.text.setText(sum + "1");
			}
		} else if (e.getSource() == number_key.two) {
			if (com || i == 0) {
				result.text.setText("2");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				result.text.setText(sum + "2");
			}

		} else if (e.getSource() == number_key.three) {
			if (com || i == 0) {
				result.text.setText("3");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				result.text.setText(sum + "3");
			}
		} else if (e.getSource() == number_key.four) {
			if (com || i == 0) {
				result.text.setText("4");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				result.text.setText(sum + "4");
			}
		} else if (e.getSource() == number_key.five) {
			if (com || i == 0) {
				result.text.setText("5");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				result.text.setText(sum + "5");
			}
		} else if (e.getSource() == number_key.six) {
			if (com || i == 0) {
				result.text.setText("6");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				result.text.setText(sum + "6");
			}
		} else if (e.getSource() == number_key.seven) {
			if (com || i == 0) {
				result.text.setText("7");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				result.text.setText(sum + "7");
			}
		} else if (e.getSource() == number_key.eight) {
			if (com || i == 0) {
				result.text.setText("8");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				result.text.setText(sum + "8");
			}
		} else if (e.getSource() == number_key.nine) {
			if (com || i == 0) {
				result.text.setText("9");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				result.text.setText(sum + "9");
			}
		}
		/*
		 * 对于0这个按钮有一定的说法，在此程序中不会出现如00000这样的情况，加的判断条件就是
		 * 如果text中的数值=0就要判断在这个数值中是否有.存在?如果有那么就在原来数值基础之上添加0;否则保持原来的数值不变
		 */
		else if (e.getSource() == number_key.zero) {
			if (com || i == 0) {
				result.text.setText("0");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				if (Float.parseFloat(sum) > 0 || Float.parseFloat(sum) < 0) {
					result.text.setText(sum + "0");
				} else {
					if (sum.trim().indexOf(".") == -1) {
						result.text.setText(sum);
					} else {
						result.text.setText(sum + "0");
					}
				}
			}
		} else if (e.getSource() == number_key.ce) {
			result.text.setText("0");
			i = 0;
			com = true;
		} else if (e.getSource() == number_key.tzero) {
			if (com || i == 0) {
				result.text.setText("0");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				if (Float.parseFloat(sum) > 0 || Float.parseFloat(sum) < 0) {
					result.text.setText(sum + "00");
				} else {
					if (sum.trim().indexOf(".") == -1) {
						result.text.setText(sum);
					} else {
						result.text.setText(sum + "00");
					}
				}
			}
		}
		/*
		 * 本程序不会让一个数值中出现2个以上的小数点.具体做法是:判断是否已经存在.存在就不添加, 不存在就添加.
		 */
		else if (e.getSource() == number_key.point) {
			if (com || i == 0) {
				result.text.setText("0.");
				com = false;
				i = 1;
			} else {
				sum = result.text.getText();
				if (sum.trim().indexOf(".") == -1) {
					result.text.setText(sum + ".");
				} else {
					result.text.setText(sum);
				}

			}
		}//获得点击+之前的数值
		else if (e.getSource() == number_key.plus) {
			com = true;
			i = 0;
			total = Double.parseDouble(result.text.getText());
			symbol = 1;
		}//获得点击-之前的数值
		else if (e.getSource() == number_key.sub) {
			com = true;
			i = 0;
			total = Double.parseDouble(result.text.getText());

			symbol = 2;
		}//获得点击*之前的数值
		else if (e.getSource() == number_key.mul) {
			com = true;
			i = 0;
			total = Double.parseDouble(result.text.getText());
			System.out.println(total);
			symbol = 3;
		}//获得点击/之前的数值
		else if (e.getSource() == number_key.div) {
			com = true;
			i = 0;
			total = Double.parseDouble(result.text.getText());
			symbol = 4;
		} else if (e.getSource() == number_key.equal) {
			switch (symbol) {
			case 1://计算加法
			{
				double ad = total + Double.parseDouble(result.text.getText());
				result.text.setText(ad + "");
				i = 0;
				sum = "";
				break;
			}
			case 2://计算减法
			{
				double ad = total - Double.parseDouble(result.text.getText());
				result.text.setText(String.valueOf(ad));
				i = 0;
				sum = "";
				break;
			}
			case 3://计算乘法
			{
				double ad = total * Double.parseDouble(result.text.getText());

				result.text.setText(ad + "");
				i = 0;
				sum = "";
				break;
			}
			case 4://计算除法
			{
				double ad = total / Double.parseDouble(result.text.getText());
				result.text.setText(ad + "");
				i = 0;
				sum = "";
				break;
			}
			}
			System.out.println(com);
		}
	}

	public static void main(String[] args) {
		Calculator calculator = new Calculator();
		calculator.show();
	}
}