Package in Java

 

Package in java

A package is nothing but a physical folder structure (directories) that contains a group of related classes, interfaces, and sub-packages according to their functionality.

- Using package keyword user can create user-defined package.

For example:

package myPackage;

public class A {

      // class body

}

Advantage of using packages in Java

1. Maintenance: Java packages are used for proper maintenance. 

2. Reusability: We can place the common code in a common folder so that everybody can check that folder and use it whenever needed.

3. Name conflict: Packages help to resolve the naming conflict between the two classes with the same name.

4. Organized: It also helps in organizing the files within our project.

5. Access Protection: A package provides access protection

Types of packages

Packages can be categorized in two types :

1. User defined packages

2. Built-in packages

1. User-defined Package

The package which is defined by the user is called a User-defined package. It contains user-defined classes and interfaces.

Creating of Package .

 Example: 

 

 package mypack;

 class Test {

      ...

   }

2. Predefined Packages  (Built-in Packages)

Predefined packages in java are those which are developed by Sun Microsystem or Java. They are also called built-in packages in java.

Ex : Java.lang: he Java language package consists of java classes and interfaces that form the core of the Java language and the JVM. It is a fundamental package that is useful for writing and executing all Java programs.

compilation  package in Java

Syntax:

To Compile the application:  javac -d directory javafilename

1. Here, javac means java compiler.

2. -d means directory. It creates the folder structure.

3. .(dot) means the current directory. It places the folder structure in the current working directory.

For example: javac -d. className.java // Here, className.java is the file name.

How to Run package in Java

Syntax:

java completePackageName.className

Importing packages in Java

There are three approaches to import one package into another package in Java.

1. import package.*;

2. import package.classname;

3. Using fully qualified name.