Java Packages

JK1536 
Created at Jul 17, 2023 07:11:32
Updated at May 10, 2024 14:03:23 
  1,173   0   0  

Java Packages & API

A package in Java is used to group related classes. Think of it as a folder in a file directory. We use packages to avoid name conflicts, and to write a better maintainable code. Packages are divided into two categories:

  • Built-in Packages (packages from the Java API)
  • User-defined Packages (create your own packages)

Built-in Packages

The Java API is a library of prewritten classes, that are free to use, included in the Java Development Environment.

The library contains components for managing input, database programming, and much much more. The complete list can be found at Oracles website: https://docs.oracle.com/javase/8/docs/api/.

The library is divided into packages and classes. Meaning you can either import a single class (along with its methods and attributes), or a whole package that contain all the classes that belong to the specified package.

To use a class or a package from the library, you need to use the import keyword:

import package.name.Class;   // Import a single class
import package.name.*;   // Import the whole package

Import a Class

If you find a class you want to use, for example, the Scanner class, which is used to get user input, write the following code:

import java.util.Scanner;

In the example above, java.util is a package, while Scanner is a class of the java.util package.

To use the Scanner class, create an object of the class and use any of the available methods found in the Scanner class documentation. In our example, we will use the nextLine() method, which is used to read a complete line:

import java.util.Scanner;

class MyClass {
  public static void main(String[] args) {
    Scanner myObj = new Scanner(System.in);
    System.out.println("Enter username");

    String userName = myObj.nextLine();
    System.out.println("Username is: " + userName);
  }
}

Import a Package

There are many packages to choose from. In the previous example, we used the Scanner class from the java.util package. This package also contains date and time facilities, random-number generator and other utility classes.

To import a whole package, end the sentence with an asterisk sign (*). The following example will import ALL the classes in the java.util package:

import java.util.*;

User-defined Packages

To create your own package, you need to understand that Java uses a file system directory to store them. Just like folders on your computer:

└── root
  └── mypack
    └── MyPackageClass.java

MyPackageClass.java

package mypack;
class MyPackageClass {
  public static void main(String[] args) {
    System.out.println("This is my package!");
  }
}

Save the file as MyPackageClass.java, and compile it:

C:\Users\Your Name>javac MyPackageClass.java

Then compile the package:

C:\Users\Your Name>javac -d . MyPackageClass.java

This forces the compiler to create the "mypack" package.

The -d keyword specifies the destination for where to save the class file. You can use any directory name, like c:/user (windows), or, if you want to keep the package within the same directory, you can use the dot sign ".", like in the example above.

Note: The package name should be written in lower case to avoid conflict with class names.

 

When we compiled the package in the example above, a new folder was created, called "mypack".

To run the MyPackageClass.java file, write the following:

C:\Users\Your Name>java mypack.MyPackageClass

The output will be:

This is my package!

 



Tags: Java Java Packages Share on Facebook Share on X

◀ PREVIOUS
Java Abstract Classes and Methods

▶ NEXT
Java Inheritance (Subclass and Superclass)

  Comments 0
OTHER POSTS IN THE SAME CATEGORY

Java Servlet Example

(created at Feb 19, 2024)

How do I replace content that based on the HTML UI Template

(created at Feb 12, 2024)

Creating a simple Java Servlet (Web Server Page) with Apache Maven on Microsoft Windows

(created at Jan 28, 2024)

Dataset of California Foodbanks

(updated at Feb 12, 2024)

Java Tutorials associated with AP Computer Science A

(updated at Jun 15, 2024)

Java Inner Classes

(updated at May 10, 2024)

Java Polymorphism

(created at Jul 18, 2023)

Java Inheritance (Subclass and Superclass)

(updated at May 10, 2024)

Java Abstract Classes and Methods

(updated at Jan 02, 2024)

Java Classes and Objects

(updated at May 10, 2024)

Java Recursion

(updated at May 10, 2024)

Java Scope

(updated at May 10, 2024)

Java Methods

(updated at May 10, 2024)

Java Arrays

(updated at May 13, 2024)

Java While Loop/Do While Loop/For Loop/For-Each Loop/Break/Continue

(updated at May 13, 2024)

Java Switch Statements

(updated at May 15, 2024)

Java Short Hand If...Else (Ternary Operator)

(updated at May 15, 2024)

Java If ... Else

(updated at May 15, 2024)

Java Math

(updated at May 15, 2024)

Java Variables

(updated at May 15, 2024)

Java Comments

(updated at May 15, 2024)

The Print() Method

(updated at May 10, 2024)

Java Syntax

(updated at May 15, 2024)

UPDATES

LoL Worldcup - Worlds 2024 Finals Opening Ceremony Presented by Mastercard ft. Linkin Park, Ashnikko and More!

(created at Nov 18, 2024)

The hippie perm of NewJeans' Danielle 

(updated at Nov 15, 2024)

Danielle was featured on the UK Fashion Pop Magazine cover

(updated at Nov 15, 2024)

IU Photos from her family trip

(updated at Nov 09, 2024)

Men vs. Women Taekwondo Sparring - Beautiful Taekwondo Star Tammy's Dazzling Roundhouse Kicks

(updated at Nov 09, 2024)

Legendary Taekwondo Match of the Korean National Sports Festival in High School Division

(updated at Nov 09, 2024)

Legendary Taekwondo 540 degree Kick - Champion Hyun-goo Noh

(created at Nov 09, 2024)

The difference between Equation and Formula

(created at Nov 08, 2024)

Lengendary Turkish Taekwondo player Tazegul at 2015 WTF World Taekwondo Championships

(updated at Nov 08, 2024)

World Rank #2 - Turkey TKD Legend Servet Tazegül

(created at Nov 07, 2024)

Irvine Restaurant American-Style Vietnamese Food Brodard (ft. Ultimate Spring Roll)

(updated at Nov 03, 2024)

Block unwanted URLs for comfortable web browsing with Chrome Addon - URL Blocker

(updated at Nov 01, 2024)

The Gigant Cowboys of Virginia City, Nevada 1889 - AI Generated Photos

(updated at Oct 28, 2024)

Sushi Koto: The "Ohtani" Sushi Spot in Irvine

(created at Oct 26, 2024)

Modern Web Indexing Technology - IndexNow

(updated at Oct 24, 2024)

Key Differences in Gen Z/Alpha/Zalpha based on Upbringing and Life Experiences

(updated at Oct 22, 2024)

Zalpha Generation: A New Term for the Children of Gen Z and Millennials

(updated at Oct 22, 2024)

Zalpha: A Global Trend, Not Just a Distant Concept

(updated at Oct 22, 2024)

The Generation Corona (+ Gen Z) is grappling with how to communicate and live alongside Gen Alpha

(updated at Oct 21, 2024)

Porto's Bakery in Buena Park: A Review from Irvine

(created at Oct 20, 2024)

Starship, Super Heavy, Successful Ground Landing

(updated at Oct 19, 2024)

Understanding Texas A&M - a leading research university, receiving significant funding from both the government and private sector

(updated at Oct 18, 2024)

Exploring UC Davis (aka UCD) - Schools and Majors

(updated at Oct 16, 2024)

AI Generated One-Punch Man with old school style TV shows

(updated at Oct 15, 2024)

One-Punch Man Analysis: The Bald Cape Hero

(updated at Oct 15, 2024)

Why One-Punch Man is a Great Action Anime?

(updated at Oct 15, 2024)

The War of Dogs and Cats - AI-Generated Video by AlgoContent

(updated at Oct 15, 2024)

Dreamy indie band Room402's song "Like the Moon in the Daytime" with AI-generated video

(updated at Oct 15, 2024)

One-Punch Man's Saitama: Motivational Quotes and the Hero's Story

(updated at Oct 13, 2024)

Cream Pan: A Must-Visit Japanese Bakery in Fountain Valley

(created at Oct 13, 2024)

NewJeans - Chicago Live at Lollapalooza 2023

(updated at Oct 12, 2024)

One-Punch Man: Saitama's Promotion Journey and the Final Goal as a Hero

(updated at Oct 12, 2024)

One-Punch Man Combat Power Rankings

(created at Oct 12, 2024)

Difference in HEAD and GET for HTTP Request - why HEAD Request could be used for DDoS Attack?

(updated at Oct 11, 2024)

AI Generated Sailor Moon Video - In the name of justice, I will not forgive you!

(updated at Oct 11, 2024)

Snack that makes my mouth happy when winter comes from the U.S - Hot Pockets

(updated at Oct 11, 2024)

One-Punch Man Crafted by AI - Witness the Limitless Power of Sora AI

(updated at Oct 11, 2024)

My chrome browser is annoying me by Language - How do I change the default language?

(updated at Oct 11, 2024)

AI-Generated Berserk: A Majestic Sight

(updated at Oct 11, 2024)

Global Electronic Medicine Trends and Market Outlook 

(updated at Oct 09, 2024)

What is Google Analytics?

(updated at Oct 09, 2024)

Understanding the Key Differences Between GIS and LBS: Purpose, Technology, and Applications

(updated at Oct 09, 2024)

The Evolution and Applications of Geographic Information Systems: From Thematic Mapping to Efficient Data Analysis and Management

(created at Oct 09, 2024)

Quantum computer and qubit generation method

(updated at Oct 08, 2024)

Green Premium, Eco-Certified Building

(updated at Oct 08, 2024)

Why Two Path Authentication is Essential - My Microsoft Account is Gone!

(updated at Oct 08, 2024)

Amazon's Return-to-Office Mandate: A Bold Move or a Step Backwards?

(updated at Oct 08, 2024)

Exploring UC Merced (aka UCM) - Schools and Majors

(updated at Oct 08, 2024)

Understanding Rose-Hulman Institute of Technology

(updated at Oct 08, 2024)

Understanding Rensselaer Polytechnic Institute based in New York

(updated at Oct 08, 2024)