Java:计算器小程序

   描述：一个简单的计算器小程序 可以实现+、-、*、/运算。具有清零和退格的功能。

   主要是熟悉一下javaGUI编程以及内部类的相关知识

   计算器面板类实现如下:

package calculator;

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

public class CalculatorPanel extends JPanel {
	private JLabel display;
	private JPanel buttonPanel;
	private JPanel toolPanel;
	private JPanel panel;
	private double result;
	private String lastCommand;
	private boolean cls;

	public CalculatorPanel(){
		setLayout(new BorderLayout());
		result = 0;          //结果
		lastCommand = "=";  //上一个运算符
		cls = true;        //清屏标识符

		//add display
		display = new JLabel("0");
		add(display, BorderLayout.NORTH);


		ActionListener insert = new InsertAction();
		ActionListener command = new CommandAction();

		//add the button to a panel
		panel = new JPanel();
		panel.setLayout(new GridLayout(4, 4));
		addButton(panel,"7", insert);
		addButton(panel,"8", insert);
		addButton(panel,"9", insert);
		addButton(panel,"/", command);

		addButton(panel,"4", insert);
		addButton(panel,"5", insert);
		addButton(panel,"6", insert);
		addButton(panel,"*", command);

		addButton(panel,"1", insert);
		addButton(panel,"2", insert);
		addButton(panel,"3", insert);
		addButton(panel,"-", command);

		addButton(panel,"0", insert);
		addButton(panel,".", insert);
		addButton(panel,"=", command);
		addButton(panel,"+", command);

		//create toolPanel
		toolPanel = new JPanel();
		toolPanel.setLayout(new GridLayout(1, 2));
		addButton(toolPanel,"AC", command);
		addButton(toolPanel,"BACK", command);

		//add panel and toolPanel to buttonPanel
		buttonPanel = new JPanel();
		buttonPanel.setLayout(new BorderLayout());
		buttonPanel.add(toolPanel, BorderLayout.NORTH);
		buttonPanel.add(panel,BorderLayout.CENTER);	

		//add buttonPanel to CalculatorPanel
		add(buttonPanel,BorderLayout.CENTER);
	}


	private void addButton(JPanel panel,String label,ActionListener listener)
	{
		JButton button =new JButton(label);
		button.addActionListener(listener);
		panel.add(button);
	}

	private class InsertAction implements ActionListener {

		@Override
		public void actionPerformed(ActionEvent e) {
			// TODO 自动生成的方法存根
			String input = e.getActionCommand();
			if(cls){
				if(!input.equals("."))//输入不是.才清屏
					display.setText("");
				cls = false;
			}
			display.setText(display.getText() + input);
		}		
	}

	private class CommandAction implements ActionListener {

		@Override
		public void actionPerformed(ActionEvent e) {
			// TODO 自动生成的方法存根
			String command = e.getActionCommand();
			
			if(command.equals("AC")){
				display.setText("0");
				result =0;
				lastCommand = "=";
				cls = true; 
				return;
			}else if(command.equals("BACK")){
				String str = display.getText();
				str = str.substring(0, str.length()-1);
				if(str.isEmpty()) {str = "0";cls = true;}
				display.setText(str);
				return;
			}

			if(cls){
				if(command.equals("-"))
				{
					display.setText(command);
					cls = false;
				}
				else lastCommand = command;
			}
			else{
				calculate(Double.parseDouble(display.getText()));
				lastCommand = command;
				cls = 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;
		else if(lastCommand.equals("=")) result = x;

		display.setText(""+result);
	}
}

效果图：