APPLETS AND MULTIMEDIA - Introduction to Java Programming - page 692

The java.net.URL class was used to locate a text file on the Internet in Section 14.13. It
can also be used to locate image files and audio files on the Internet. In general, a URL object
is a pointer to a “resource” on a local machine or a remote host. A resource can be a file or a
directory.
The URL class can be used to locate a resource file from a class in a way that is independent
of the file's location, as long as the resource file is located in the class directory. Recall that
the class directory is where the class is stored. To obtain the URL object for a file from a class,
use the following statement in the applet or application:

Directory

.
.
.
Class metaObject = this .getClass();
URL url = metaObject.getResource(resourceFilename);
.
.
.

An applet or
application

A resource file

The getClass() method returns an instance of the java.lang.Class class for the current
class. This instance is automatically created by the JVM for every class loaded into the mem-
ory. This instance, also known as a meta object , contains the information about the class file
such as class name, constructors, and methods. You can obtain a URL object for a file in the
class path by invoking the getResource(filename) method on the meta object. For exam-
ple, if the class file is in c:\book , the following statements obtain a URL object for
c:\book\image\us.gif .

meta object

.
.
.
Class metaObject = this .getClass();
URL url = metaObject.getResource( "image/us.gif" );
.
.
.

C:\book

An applet or
application

image

us.gif

You can now create an ImageIcon using

ImageIcon imageIcon = new ImageIcon(url);

Listing 18.11 gives the code that displays an image from image/us.gif in the class directory.
The file image/us.gif is under the class directory, and its URL object is obtained using the
getResource method (line 5). A label with an image icon is created in line 6. The image
icon is obtained from the URL object.

L ISTING 18.11 DisplayImageWithURL.java
1 import javax.swing.*;
2
3 public class DisplayImageWithURL extends JApplet {