calculator

import java.awt.*;
import java.awt.event.*;
import java.text.DecimalFormat;
import javax.swing.*;
public class Calculator implements ActionListener {
	JFrame frame;
	JPanel panel, panel1, panel2, panel3;
	JMenuBar mainMenu;
	JMenu mcalculator, mhelp;
	JMenuItem miquit, miabout;
	JTextField textAnswer;
	JButton btnBksp, btnCE, btnClr, btnAddSub, btnAdd, btnSub, btnMul, btnDiv,
			btnEqu, btnDot;
	JButton button[];
	//key 当前运算
	//prekey 前一次运算
	short key = -1;
	short prekey = -1;
	double answer,vard;
	boolean clickable = true;
	DecimalFormat df;
	public Calculator() {
		df = new DecimalFormat("0.##########");
		//*******************布局***************************
		// name
		frame = new JFrame("Calculor");
		// panel
		panel = new JPanel();
		frame.getContentPane().add(panel);
		panel.setLayout(new BorderLayout(10, 10));
		// mainMenu
		mainMenu = new JMenuBar();
		mcalculator = new JMenu("calculator");
		mhelp = new JMenu("help");
		mainMenu.add(mcalculator);
		mainMenu.add(mhelp);
		miquit = new JMenuItem("quit");
		miabout = new JMenuItem("about");
		mcalculator.add(miquit);
		mhelp.add(miabout);
		frame.setJMenuBar(mainMenu);
		// panel.add(mainMenu, BorderLayout.NORTH);
		// textField
		textAnswer = new JTextField(15);
		panel.add(textAnswer, BorderLayout.NORTH);
		// panel1
		btnBksp = new JButton("Bksp");
		btnCE = new JButton("CE");
		btnClr = new JButton("Clr");
		btnAddSub = new JButton("+/-");
		btnAdd = new JButton("+");
		btnSub = new JButton("-");
		btnMul = new JButton("*");
		btnDiv = new JButton("/");
		btnEqu = new JButton("=");
		btnDot = new JButton(".");
		button = new JButton[10];
		for (int i = 0; i <= 9; ++i) {
			button[i] = new JButton("" + i);
		}
		panel1 = new JPanel();
		panel1.setLayout(new GridLayout(5, 4, 10, 10));
		panel1.add(btnBksp);
		panel1.add(btnCE);
		panel1.add(btnClr);
		panel1.add(btnAddSub);
		for (int i = 7; i <= 9; ++i) {
			panel1.add(button[i]);
		}
		panel1.add(btnDiv);
		for (int i = 4; i <= 6; ++i) {
			panel1.add(button[i]);
		}
		panel1.add(btnMul);
		for (int i = 1; i <= 3; ++i) {
			panel1.add(button[i]);
		}
		panel1.add(btnSub);
		panel1.add(button[0]);
		panel1.add(btnDot);
		panel1.add(btnEqu);
		panel1.add(btnAdd);
		panel.add(panel1, BorderLayout.SOUTH);
		// JPanel tmp1 = new JPanel();
		// JPanel tmp2 = new JPanel();
		// panel.add(tmp1,BorderLayout.EAST);
		// panel.add(tmp2,BorderLayout.WEST);
		// show in the center
		// ***********************监听**********************
		btnBksp.addActionListener(this);
		btnCE.addActionListener(this);
		btnClr.addActionListener(this);
		btnAddSub.addActionListener(this);
		btnDot.addActionListener(this);
		btnAdd.addActionListener(this);
		btnSub.addActionListener(this);
		btnMul.addActionListener(this);
		btnDiv.addActionListener(this);
		btnEqu.addActionListener(this);
		for(int i=0; i<=9; ++i) {
			button[i].addActionListener(this);
		}
		//********************显示****************************************
		Dimension scrSize = Toolkit.getDefaultToolkit().getScreenSize();
		frame.setLocation((scrSize.width - frame.getSize().width) / 2,
				(scrSize.height - frame.getSize().height) / 2);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.pack();
		frame.setResizable(false);
		frame.setVisible(true);
	}
	//*************************事件处理************************************
	@Override
	public void actionPerformed(ActionEvent ae) {
		Object tmp = ae.getSource();
		try {
			for(int i=0; i<=9; ++i) {
				if(tmp == button[i] && true == clickable) {
					textAnswer.setText(textAnswer.getText() + Integer.toString(i));
				}
			}
			//小数点按钮，如果还没有小数点就加点
			if(tmp == btnDot && true == clickable) {
				boolean isDot = false;
				if(0 == textAnswer.getText().length())
					isDot = true;
				for(int i=0; i<textAnswer.getText().length(); ++i) {
					if('.' == textAnswer.getText().charAt(i)) {
						isDot = true;
						break;
					}
				}
				if(false == isDot && true == clickable) {
					textAnswer.setText(textAnswer.getText() + ".");
				}
			}
			if((tmp == btnAdd || tmp == btnSub || tmp == btnMul || tmp == btnDiv) &&
					true == clickable) {
				//根据前一种运算确定 answer值
				if(tmp == btnAdd) {
					switch (prekey){
					case 0:
						answer += Double.parseDouble(textAnswer.getText());
						break;
					case 1:
						answer -= Double.parseDouble(textAnswer.getText());
						break;
					case 2:
						answer *= Double.parseDouble(textAnswer.getText());
						break;
					case 3:
						if(0 ==Double.parseDouble(textAnswer.getText())) {
							textAnswer.setText("Error:Div by zero!");
							clickable = false;
						} else
							answer /= Double.parseDouble(textAnswer.getText());
						break;
					default:
						answer = Double.parseDouble(textAnswer.getText());
					}
					textAnswer.setText("");
					prekey = key = 0;
				}
				if(tmp == btnSub) {
					switch (prekey){
					case 0:
						answer += Double.parseDouble(textAnswer.getText());
						break;
					case 1:
						answer -= Double.parseDouble(textAnswer.getText());
						break;
					case 2:
						answer *= Double.parseDouble(textAnswer.getText());
						break;
					case 3:
						if(0 ==Double.parseDouble(textAnswer.getText())) {
							textAnswer.setText("Error:Div by zero!");
							clickable = false;
						} else
							answer /= Double.parseDouble(textAnswer.getText());
						break;
					default:
						answer = Double.parseDouble(textAnswer.getText());
					}
					textAnswer.setText("");
					prekey = key = 1;
				}
				if(tmp == btnMul) {
					switch (prekey){
					case 0:
						answer += Double.parseDouble(textAnswer.getText());
						break;
					case 1:
						answer -= Double.parseDouble(textAnswer.getText());
						break;
					case 2:
						answer *= Double.parseDouble(textAnswer.getText());
						break;
					case 3:
						if(0 ==Double.parseDouble(textAnswer.getText())) {
							textAnswer.setText("Error:Div by zero!");
							clickable = false;
						} else
							answer /= Double.parseDouble(textAnswer.getText());
						break;
					default:
						answer = Double.parseDouble(textAnswer.getText());
					}
					textAnswer.setText("");
					prekey = key = 2;
				}
				if(tmp == btnDiv) {
					switch (prekey){
					case 0:
						answer += Double.parseDouble(textAnswer.getText());
						break;
					case 1:
						answer -= Double.parseDouble(textAnswer.getText());
						break;
					case 2:
						answer *= Double.parseDouble(textAnswer.getText());
						break;
					case 3:
						if(0 ==Double.parseDouble(textAnswer.getText())) {
							textAnswer.setText("Error:Div by zero!");
							clickable = false;
						} else
							answer /= Double.parseDouble(textAnswer.getText());
						break;
					default:
						answer = Double.parseDouble(textAnswer.getText());
					}
					textAnswer.setText("");
					prekey = key = 3;
				}
			}
			if(tmp == btnEqu && true == clickable) {
				//连续按等号，则作连续运算
				if(5 == prekey) {
					if(0== key) {
						answer += vard;
						textAnswer.setText(df.format(answer));
					}
					if(1== key) {
						answer -= vard;
						textAnswer.setText(df.format(answer));
					}
					if(2== key) {
						answer *= vard;
						textAnswer.setText(df.format(answer));
					}
					if(3== key) {
						if(0 ==Double.parseDouble(textAnswer.getText())) {
							textAnswer.setText("Error:Div by zero!");
							clickable = false;
						} else
							answer /= vard;
						textAnswer.setText(df.format(answer));
					}
				} else {
					vard = Double.parseDouble(textAnswer.getText());
					switch (prekey){
					case 0:
						answer += Double.parseDouble(textAnswer.getText());
						break;
					case 1:
						answer -= Double.parseDouble(textAnswer.getText());
						break;
					case 2:
						answer *= Double.parseDouble(textAnswer.getText());
						break;
					case 3:
						if(0 ==Double.parseDouble(textAnswer.getText())) {
							textAnswer.setText("Error:Div by zero!");
							clickable = false;
						} else
							answer /= Double.parseDouble(textAnswer.getText());
						break;
					default:
						answer = Double.parseDouble(textAnswer.getText());
					}
					//把答案贴出来
					textAnswer.setText(df.format(answer));
				}
				prekey = 5;
			}
			if (tmp == btnBksp && true == clickable) {
				String s = textAnswer.getText();
				textAnswer.setText("");
				for (int i = 0; i < s.length() - 1; ++i) {
					char a = s.charAt(i);
					textAnswer.setText(textAnswer.getText() + a);
				}
			}
			//当前窗口清0
			if (tmp == btnCE) {
				textAnswer.setText("");
				clickable = true;
			}
			//Clr键要把所有都清0
			if (tmp == btnClr) {
				answer = 0;
				vard = 0;
				textAnswer.setText("");
				clickable = true;
			}
			if (tmp == btnAddSub && true == clickable) {
				boolean isNumber = true;
				String s = textAnswer.getText();
				for (int i = 0; i < s.length(); ++i) {
					if (!(s.charAt(i) >= '0' && s.charAt(i) <= '9'
							|| '.' == s.charAt(i) || '-' == s.charAt(i))) {
						isNumber = false;
						break;
					}
				}
				if (true == isNumber) {
					if ('-' == s.charAt(0)) {
						textAnswer.setText("");
						for (int i = 1; i < s.length(); ++i) {
							char a = s.charAt(i);
							textAnswer.setText(textAnswer.getText() + a);
						}
					} else {
						textAnswer.setText('-' + s);
					}
				}
			}
			
		} catch (Exception e) {
			textAnswer.setText("Error!");
			clickable = false;
		}
	}
	public static void main(String[] args) {
		new Calculator();
	}
}