Java: About Packages
This is a grouping of related classes and/or interfaces into
a library.
How to Import a Pacakge
If you need a class in a package, then the package must be imported into
the java code have the following at the top of the program:
import package_name
How to reference a class not in an imported package
If not imported then the call to the class must explicitly reference the
pacakge (e.g. the Graphics class in the package java.awt would be called
as java.awt.Graphics).
Create your own package called MyPack
- The first line of each of the source files:
pacakge MyPack
- Compile each source file using the -d option to indicate
where to place the directory structure for the new classes.
javac -d classes_dir file1.java
- After compilation a subdirectory in the classes_dir directory
called MyPack will be created that contains the files file1.class,
etc.
- Now you can import this package import MyPack
Some Java Packages
- java.applet
This package includes classes for use in an applet.
- java.awt
This is the Abstract Windowing Toolkit package (awt) and contains graphical
GUI components usch as panels, graphics, menus, buttons, etc.
- java.io
This package contains classes to perform input and output operations
to files.
- java.lang
This is the basic Java package that contains the most basic class Object
and also contains Thread, Exception, System, Integer, Float, Math,
String classes.
- java.net
This package supports TCP/IP network protocols.
IMPORTANT All applets are subclasses of the class Applet which is
part of the package java.applet.
public class HelloAgainApplet extends java.applet.Applet{
}
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