Packages Basics

Packages are containers for classes that are used to keep the class namespace partitioned. The package is both a naming and a visibility control mechanism. We can control the visibility of classes within a package using the various access specifiers.

Defining a Package

To define a package the package command is included as the first statement in a Java source file. Any classes declared within that file will belong to the specified package. The package statement defines a name space in which classes are stored.

package pakage_name;

/* If you omit the package statement, the class names are put into the default package, which has no name.*/

Java uses file system directories to store packages. For example, the .class files for any classes you declare to be part of MyPackage must be stored in a directory called MyPackage.

Package Hierarchy

To create a hierarchy of packages, separate each package name from the one above it by use of a period.


package pkg1[.pkg2[.pkg3]];

/* A package hierarchy must be reflected in the file system of your Java development system. */

Importing Packages

Java includes the import statement to bring certain classes, or entire packages, into visibility. Once imported, a class can be referred to directly, using only its name.


In a Java source file, import statements occur immediately following the package statement (if it exists) and before any class definitions. This is the general form of the import statement:
import pkg1[.pkg2].(classname | *);

/* the star form may increase compilation time—especially if you import several large packages.For this reason it is a good idea to explicitly name the classes that you want to use rather than importing whole packages. However, the star form has absolutely no effect on the run-time performance or size of your classes.*/