Java Package

 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.

 Advantage of Java Package

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.

 simple example of java package

package mypack;  

public class Simple{  

 public static void main(String args[])

{  

    System.out.println("Welcome to package");  

   }  

}

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.

    1) Using package name.*

If you use package.* then all the classes and interfaces of this package will be accessible but not subpackage.

The import keyword is used to make the classes and interface of another package accessible to the current package.

Example


package pack;  

public class A{  

  public void msg(){System.out.println("Hello");}  

}  

package mypack;  

import pack.*;  

  

class B{  

  public static void main(String args[]){  

   A obj = new A();  

   obj.msg();  

  }  

}  


2) Using packagename.classname

If you import package.classname then only declared class of this package will be accessible.

Example

  package pack;  

public class A{  

  public void msg(){System.out.println("Hello");}  

}  

package mypack;  

import pack.A;  

  

class B{  

  public static void main(String args[]){  

   A obj = new A();  

   obj.msg();  

  }  

}  

3) Using fully qualified name

If you use fully qualified name then only declared class of this package will be accessible. Now there is no need to import. But you need to use fully qualified name every time when you are accessing the class or interface.

It is generally used when two packages have same class name e.g. java.util and java.sql packages contain Date class.

Example

package pack;  

public class A{  

  public void msg(){System.out.println("Hello");}  

}  

package mypack;  

class B{  

  public static void main(String args[]){  

   pack.A obj = new pack.A();//using fully qualified name  

   obj.msg();  

  }  

}  


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