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{
}