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Java Package

A java package is a group of similar types of classes, interfaces and sub-packages.

Package in java can be categorized in two form, built-in package and user-defined package.

There are many built-in packages such as java, lang, awt, javax, swing, net, io, util, sql etc.

Here, we will have the detailed learning of creating and using user-defined packages.

Advantage of Java Package

1) Java package is used to categorize the classes and interfaces so that they can be easily maintained.

2) Java package provides access protection.

3) Java package removes naming collision.

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Simple example of java package

The package keyword is used to create a package in java.

1. //save as Simple.java  
2. package mypack;  
3. public class Simple{  
4.  public static void main(String args[]){  
5.     System.out.println("Welcome to package");  
6.    }  
7. }  

How to compile java package

If you are not using any IDE, you need to follow the syntax given below:

1. javac -d directory javafilename  

For example

1. javac -d . Simple.java  

The -d switch specifies the destination where to put the generated class file. You can use any directory name like /home (in case of Linux), d:/abc (in case of windows) etc. If you want to keep the package within the same directory, you can use . (dot).

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How to run java package program

You need to use fully qualified name e.g. mypack.Simple etc to run the class.

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To Compile: javac -d . Simple.java

To Run: java mypack.Simple

Output:Welcome to package

The -d is a switch that tells the compiler where to put the class file i.e. it represents destination. The . represents the current folder.