The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
Whenever a Java applet needs to load data from a file that is specified with a relative URL (a URL that doesn't completely specify the file's location), the applet usually uses either the code base or the document base to form the complete URL.
The code base, returned by the JApplet
getCodeBase
method, is a URL that specifies the directory from which the applet's classes were loaded. For locally deployed applets, the getCodeBase
method returns null.
The document base, returned by the JApplet
getDocumentBase
method, specifies the directory of the HTML page that contains the applet. For locally deployed applets, the getDocumentBase
method returns null.
Unless the <applet>
tag specifies a code base, both the code base and document base refer to the same directory on the same server.
Data that the applet might need, or needs to rely on as a backup, is usually specified relative to the code base. Data that the applet developer specifies, often by using parameters, is usually specified relative to the document base.
The JApplet
class defines convenient forms of image-loading and sound-loading methods that enable you to specify images and sounds relative to a base URL. For example, assume an applet is set up with one of the directory structures shown in the following figure.
To create an Image
object that uses the a.gif
image file under imgDir
, the applet can use the following code:
Image image = getImage(getCodeBase(), "imgDir/a.gif");