布局的例子（边框布局&网格布局）

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
/** 
 * @author binbin
 *function:简易计算器
 */

public class Calculator {
	public static void main(String[] args)
	{
		EventQueue.invokeLater(new Runnable()
		{
			public void run()
			{
				CalculatorFrame frame= new CalculatorFrame();
				frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
				frame.setVisible(true);
			}
		});
	}

}

/**
 *A frame with acalculator panel;
 */
class CalculatorFrame extends JFrame
{
	public CalculatorFrame()
	{
		setTitle("Calculator");
		CalculatorPanel panel = new CalculatorPanel();
		add(panel);
		pack();
	}
}

/**
 * A panel with calculator buttons and a result display;
 */
class CalculatorPanel extends JPanel
{
	public CalculatorPanel()
	{
		setLayout(new BorderLayout());
		
		result = 0;
		lastCommand = "=";
		start  = true;
		
		//add the display
		
		display = new JButton("0");
		display.setEnabled(false);
		add(display,BorderLayout.NORTH);
		
		ActionListener insert = new InsertAction();
		ActionListener command = new CommandAction();
		
		//add the buttons in a 4*4 grid
		
		panel = new JPanel();
		panel.setLayout(new GridLayout(4,4));
		
		addButton("7",insert);
		addButton("8",insert);
		addButton("9",insert);
		addButton("/",command);
		
		addButton("4",insert);
		addButton("5",insert);
		addButton("6",insert);
		addButton("*",command);
		
		addButton("1",insert);
		addButton("2",insert);
		addButton("3",insert);
		addButton("-",command);
		
		addButton("0",insert);
		addButton(".",insert);
		addButton("=",command);
		addButton("+",command);
		
		add(panel,BorderLayout.CENTER);
	}
	/**
	 * Adds a button to the center panel;
	 * @param label
	 * @param listener
	 */
	private void addButton(String label,ActionListener listener)
	{
		JButton button = new JButton(label);
		button.addActionListener(listener);
		panel.add(button);
	}
	
	/**
	 * This action inserts the button action string to the end of the display text.
	 */
	private class InsertAction implements ActionListener
	{
		public void actionPerformed(ActionEvent event)
		{
			String input = event.getActionCommand();
			if(start)
			{
				display.setText("");
				start = false;
			}
			display.setText(display.getText() + input);
		}
	}
	
	/**
	 * This action executes the command that the button action string denotes.
	 */
	private class CommandAction implements ActionListener
	{
		public void actionPerformed(ActionEvent event)
		{
			String command = event.getActionCommand();
			
			if(start)
			{
				if(command.equals("-"))
				{
					display.setText(command);
					start = false;
				}
				else 
					lastCommand = command;
			}
			else
			{
				calculate(Double.parseDouble(display.getText()));
				lastCommand = command;
				start = true;
			}
		}
	}
	
	/**
	 * Carries out the pending calculation.
	 * @param x
	 */
	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);
	}
	
	private JButton display;
	private JPanel panel;
	private double result;
	private String lastCommand;
	private boolean start;	
}