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Packages in Java: All you Need to Know
Sienna Roberts 31 March 2023Packages in Java are collections of related classes, interfaces, and sub-packages. This blog will explain the use of Packages in Java programming, a powerful feature which allows you to encapsulate objects in Java and complex codes.
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Table of Contents
Created by accident, Java was produced as a result of cleaning up the C++ code while building a set-top box. A language freed from the concept of pointers as their presence compromises the security, increasing the complexity of the language in the process. Going deeper, one element, which aims to control access and prevent naming conflicts, is referred to as a Package in Java.
A Package is a mechanism in Java utilised to encapsulate class groups, interfaces and sub-packages. Check out this blog on Packages in Java, explaining What it is and providing a complete tutorial on creating, importing, and compiling packages.
Table of Contents
1) What are Packages in Java?
2) Working mechanism of Packages in Java
3) Examples of Packages in Java
a) Built-in Packages
b) User-defined Packages
4) Conclusion
What are Packages in Java?
A Package in Java is purposed for grouping classes related to one another. Packages can be considered a directory for files and are implemented to avoid naming conflicts and produce better-quality code in maintenance.
A generally followed protocol is to group related classes into a Package, then write an import class from available Packages such as ‘import java.util.*’. In this statement, the asterisk symbol, the ‘wildcard’, is included to import all classes in the ‘util’ package.
An advantage of Package classes is that they can also be reused as many times as desired in our program. The names of Packages are very similar to the directory structure, such as if a package name is ‘city.people.area’, there exist three directories, namely ‘city’, ‘people’ and ‘area’. Additionally, the directory ‘city’ is accessible using the ‘CLASSPATH’ variable because the parent directory’s path of ‘city’ exists inside CLASSPATH. The central idea here is to ensure that classes are easily locatable.
Working mechanism of Packages in Java
In Java, Packages play a crucial role in organising and categorising classes, allowing for better code management. The syntax for referencing classes within Packages follows a hierarchical structure, exemplified by "Package_name.sub_package_name.class_name."
Built-in Packages in Java
Java's built-in Packages, such as java.awt.event, demonstrate the hierarchical structure. For instance, in the Package java.awt.event, 'java' is the Package name, 'awt' is the subpackage, and 'event' is the class name.
User-defined Packages in Java
Creating user-defined Packages involves understanding the Java file system directory. For instance, 'University.Department.Staff' signifies the 'University' as the Package name, 'Department' as the subpackage, and 'Staff' as the class name.
Importing Packages in Java
To utilise classes or Packages, the 'import' keyword is essential. One can import a specific class from a Package, an entire package, or use the complete qualified name without importing.
Example 1: Importing Built-in Packages
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import java.util.*; import java.util.Scanner;
public class PackageImportExample { public static void main(String args[]) throws Exception { Scanner scanObj = new Scanner(System.in); System.out.print("Enter Your UserName:"); String sName = scanObj.nextLine(); System.out.println("UserName is: " + sName); scanObj.close();
Date currdate = new Date(); System.out.println(currdate.toString());
java.net.InetAddress ipAddress=java.net.InetAddress.getLocalHost(); System.out.println("My IP Address :"+ipAddress.getHostAddress()); } } |
Example 2: Creating user-defined Packages
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package university;
public class WelcomeMessage { public void ShowMessage() { System.out.println("Welcome to our University"); } } |
Example 3: Creating sub-packages
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package university.department;
public class DepartmentGoal { public void DepartmentGoalMessage() { System.out.println("Department Message Displayed"); } } |
Example 4: Creating Classes in Sub-packages
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package university.department; public class Staff { public void AddStaff() { System.out.println("Staff Added!"); } public void RemoveStaff() { System.out.println("Staff Removed!"); } } |
Example 5: Using user-defined Packages in Java Program:
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import university.department.Staff; public class MyOwnPackageExample { public static void main(String args[]) { Staff mystaff = new Staff(); mystaff.AddStaff(); mystaff.RemoveStaff(); } } |
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Examples of Packages in Java
Built-in Package
The Java API is a library containing prewritten classes that are free and included within the Java Development Environment (JDE). This library is split into classes and packages, meaning that either one class can be imported or a complete Package that includes all the classes belonging to the specified Package.
To use a Package or class from the Java library, the 'import' keyword must be used in the following way:
To import one single class: import package.name.class;
To import the complete package: import package.name.*;
User-defined Packages
To make your Package, it must be understood that Java has a file system directory for storage, similar to the folder system in your computer. To create your Package, just use the 'package' keyword. For example, 'package mypackage;'.
Conclusion
You have been introduced to the concept of a Package in Java so far. This blog has briefly illustrated the classes involved and the protocol for importing Packages. You have also learnt that Java provides you with built-in and the ability to create your Packages. Packages in Java essentially resemble the file directory structure in a computer system and enable access to public classes in other packages.
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Frequently Asked Questions
Why are packages important in Java programming?
Packages in Java are crucial for organising and structuring code, preventing naming conflicts, and enhancing code readability. They facilitate modular development, code reuse, and effective management of large-scale projects.
What is Java Util Package?
The Java Util Package is a fundamental Package in Java that provides utility classes and interfaces for basic data structures, date and time handling, input/output operations, and more. It includes commonly used functionalities, such as collections, arrays, and the Date class, making it a vital component of Java programming for diverse applications.
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