eventhandlingdemo1.java

JAVA程序设计课程中各章节的程序实例。

/**
*A simple but very good event handling program,pay more attention!
*implements Listener Interface
*2004.12.28. xhcprince
*/

import java.awt.*;
import java.awt.event.*;

public class EventHandlingDemo1 extends Frame implements ActionListener
{
	private Button b1;
	private Label l1;
	private int clicked;
	final String s = "Number of times button clicked = ";
	
	public EventHandlingDemo1(String strName)
	{
		super(strName);	//pay more attention to the common form of such program!
		
		Panel p = new Panel();
		b1 = new Button("Click here");
		
		p.setLayout(new FlowLayout());
		p.add(b1);
		
		l1 = new Label(s + clicked, Label.CENTER);
		
		add(p);
		add(l1,"North");	//it's l1 not 11 !
		
		b1.addActionListener(this);	
	/*---------------------------------------------------------------------------
		Here,whenever Button b1 is clicked,it generates an event and is notified
		to listener object that is "this",this refers to the current class
		(Interface for the click of a button is ActionListener).So "this" is an 
		event listener object and b1 is the event source
	---------------------------------------------------------------------------*/
	}
	
	/*---------------------------------------------------------------------------
		The ActionListener interface declares a single function,
		that is the actionPerformed() function,the argument of which is the 
		object of the class ActionEvent.
	---------------------------------------------------------------------------*/
	public void actionPerformed(ActionEvent e)
	{
		String str = e.getActionCommand();	//pay attention!
	/*---------------------------------------------------------------------------
		The function getActionCommand() returns the label of the button that is
		the source of the event
	---------------------------------------------------------------------------*/
		
		if("Click here".equals(str))	//pay attention!
		{
			++clicked;
			l1.setText(s + clicked);
		}
	}

	public static void main(String args[])
	{
		EventHandlingDemo1 obj = new EventHandlingDemo1("Taller:)");
		obj.setSize(300,300);
		obj.setVisible(true);
	}
}