Packages In Java

Modularity

Modularity is one of the main Object-oriented principles. It is a concept of breaking a program into smaller units.

Modularity can be implemented in java using packages.

Packages

• It is a way of organizing files by grouping semantically the related classes.

• It can contain classes, interfaces, and sub-packages.

• Packages are stored in the directory tree containing the package name.

• It can be created using the keyword "package".

• Helpful in managing large software systems.

• Helpful in avoiding class name collisions and providing access restrictions.

• All packages in java start with java or javax.

Design Guidelines | How to Create User Defined Package in Java

1. Package names should be in lowercase.

2. Only related classes should be inside the same package.

3. The package should be the first statement in the source file else it will lead to compile time error.

4. Package names are usually kept with a reverse internet domain name of the company. For example - the company name is Google and the domain of the company is google.com. So, the package name will be - com.google.classname.

package com.google.studentclass

Usage of Import Keyword

When a class in one package needs to use the class in a different package, the import keyword is used.

• It should precede all the class declarations.

• Tells the compiler, where to find the classes.

Basic syntax of Import Keyword

1. To import a specific class from a current subpackage. package <pkg_name>.<sub_pkg_name>.<classname>

2. To import a specific class from a current package. package <pkg_name>.<classname>;

3. To import all classes at once from the current sub package or package. package <pkg_name>.<sub_pkg_name>.*; * is a wild card character that imports all the class in the

Static Import

A static import allows you to refer to the members of another class without writing that class name. Static fields and methods can be imported using static import.

For example -

• Import all the static fields and methods of the Math class. import static java.lang.Math.*; double value = PI;

• Import a specific field or method import static java.lang.Math.abs; double value = abs(-2.8);

Core Java Packages | Pre-Defined Packages in Java

1. java.lang

2. java.util

3. java.io

4. java.math

5. java.sql

6. java.net

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created by Vaishnavi Chaurasia @TechInfinity