23: Packages Part 1 Java Programming in Urdu

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.

Example of java package 

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

Simple example of java package
The package keyword is used to create a package in java.

For run java package program:

javac -d directory javafilename 
forexample
javac -d . Simple.java 

To Compile: javac -d . Simple.java
To Run: java mypack.Simple

How to access package from another package?

There are three ways to access the package from outside the package.

1. import package.*;
2.  import package.classname; 
3. fully qualified name.

Example of package that import the packagename.*

//save by A.java  
package pack;  
public class A{  
  public void msg(){System.out.println("Hello");}  
}  



//save by B.java  
package mypack;  
import pack.*;  
  
class B{  
  public static void main(String args[]){  
   A obj = new A();  
   obj.msg();  
  }  
}  

Example of package by import package.classname

//save by A.java  
  
package pack;  
public class A{  
  public void msg(){System.out.println("Hello");}  
}  
//save by B.java  
package mypack;  
import pack.A;  
  
class B{  
  public static void main(String args[]){  
   A obj = new A();  
   obj.msg();  
  }  
} 

Example of package by import fully qualified name

//save by A.java  
package pack;  
public class A{  
  public void msg(){System.out.println("Hello");}  
}  
//save by B.java  
package mypack;  
class B{  
  public static void main(String args[]){  
   pack.A obj = new pack.A();//using fully qualified name  
   obj.msg();  
  }  
}