Packages in Java

March 28, 2023

Packages in Java Language

The packages in Java Language is nothing more than directories that gathers related classes, interfaces,
and sub-packages based on their functional relationships in java.
There are many built-in packages for the Java language.

Packages in Java

Overview of Packages :

  • Encapsulation is a key Java OOP principle that is implemented mostly through packages.
  • A large project’s classes can be organised using Java packages, which can aid in the implementation of encapsulation.

There exist two different kinds of packages :

  1. Build-in packages
  2. User-defined packages

Creating User -Defined Packages :

In java, we already have a number of pre-defined packages that contain a large number of classes and interfaces. These packages are known as Built-in packages and we can directly import them in our code.

Some commonly used built-in packages are:

  • java.io Data streams, serialisation, and the file system are all supported by this package for system input and output.
  • java.lang contains classes that are essential to the design of the Java programming language.
  • java.math Classes in this package perform arbitrary-precision integer arithmetic (BigInteger) and arbitrary-precision decimal arithmetic (BigDecimal).
  • java.util The collections framework, some internationalisation support classes, and a few utility classes are included.
  import java.util.*;
  or
  import java.util.Scanner;

abs() Function

acos() Function

addExact() Function

asin() Function

atan() Function

Creating Packages in Java Command Line :

javac -d PrepInsta java
java mob gif
java desk gif
Packages in Java Diagram

Creating User -Defined Packages :

Java also allows you to make your own packages.These are referred to as user-defined packages.

package demoPackage;
    public class demoClass
    {
        public void getMessage(String m)
        {
            System.out.println(m);
        }
    }

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After creating our own package we can use its classes in our program.

 public class Main 
    {
        public static void main(String args[]) 
        { 
            String message = "This is how User-Definded Packages work";
            demoClass object = new demoClass();
            object.getMessage(message);
        }
}

Points to Remember:

  • Either import the class or use the fully qualified class name in order to access code that is located outside the current package.
  • Using packages while coding provides code reusability benefit.
  • Packages allow us to uniquely identify a class.
  • Access control features include protected classes, default classes, and private classes.
  • They enable the hiding of classes, preventing other programmes from accessing classes intended for internal use only.
  • You can better organise your project and find related classes by using packages.

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