Introduction

A Packages in JAVA is a grouping of related classes, interfaces, and sub-packages. Built-in and user-defined packages are both available in Java. Java packages are made using the package keyword.

Java has a large number of built-in packages, such as util, lang, awt, java, swing, net, io, SQL, etc. Using the packagename.* statement, we may import every component of a package.

What is Package in Java?

A Package in Java is a grouping of interfaces, sub-packages, and classes. It facilitates the folder-based organization of your lessons and makes it simple to find and access them. More critically, it facilitates greater code reuse.

In Java, every package has its own specific name and groups its classes and interfaces into a distinct namespace.

Classes and interfaces with the same name cannot be found in the same package, although they can be found in distinct packages. Each Java package can have its own namespace, which makes this possible.

Syntax:

package nameOfPackage;

Types of Packages in Java

There are two categories in which Packages in JAVA can be placed.

1. Built-in / predefined packages
2. User-defined packages.

Built-in Packages

Numerous packages are installed automatically when Java is installed on a desktop or laptop. Packages in Java, Each of them is distinct in their own right and is able to handle a variety of jobs.

This saves us from having to rebuild everything from scratch. Below is a collection of several built-in package examples.

Core packages:

Java.lang: 

Language is referred to as lang. The Java language package is made up of Java classes and interfaces, which together make up the JVM and the Java language. All Java programs can be written and run using this core package.

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Classes, objects, Strings, Threads, predefined data types, etc. are few examples. The Java programs automatically import it.

Java.io: 

Input and output are referred to as “io.” It offers a selection of I/O streams for reading and writing data to files. A stream depicts the movement of data from one location to another.

Java util: 

Utility is denoted by util. It includes a number of practical utility classes and associated interfaces for implementing data structures including LinkedList, Dictionary, HashTable, stack, vector, calendar, and data utility.

Java.net: 

Network is referred to as net. It has interfaces and networking classes for networking operations. This module can be used to create client-server programming.

Window Toolkit and Applet

Java.awt: 

Abstract window toolkit is referred to as awt. The GUI (Graphical User Interface) components, Packages in java, such as buttons, lists, menus, and text fields, are included in the Abstract Window Toolkit packages. Using this package, programmers can create applications with vibrant screens, artwork, and other visual elements.

Java.awt.image: 

For producing graphics and colors, it has classes and interfaces.

Java.applet: 

It is utilised to make applets. On a network, applets are applications that are run from the server into the client system.

Java.text: 

Two significant classes, such as DateFormat and NumberFormat, are included in this package. To format dates and times, use the DateFormat class. Numeric values are formatted using the NumberFormat.

Java.sql: 

A structured query language is known as SQL. When connecting to databases like Oracle or Sybase and retrieving data from them, a Java program uses this package.

User-Defined Packages

Developers build user-defined packages to accommodate various application requirements. User-defined packages, to put it simply, are those that the users define. Java files such as classes, interfaces, and other packages (referred to as a sub-package) can all be found inside a package.

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Creating Packages in Java

In Java programming, the keyword “package” is supported and is used to create user-defined packages. It takes the general shape as follows:

package packageName;

The package name in this instance is packageName. A Java source code file must begin with a package statement and then one or more classes.

For example:

package myPackage;

public class A {

      // class body

}

How to Compile Packages in Java?

If you are not using an Eclipse IDE, you should use the following syntax:

Syntax:

To Compile the application:  javac -d directory javafilename

1.Java compiler is referred to as javac in this context.

-d stands for directory. It establishes the folder hierarchy.

The current directory is denoted by.(dot). The folder hierarchy is added to the active working directory.

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

As a result, if an application has a package declaration, you must compile it.

You may see the folder hierarchy in your system after the compilation looks like this:

com
  |—> scientecheasy
      |——> java
        |——> corejava
            |——> Example.class

How to run Java Package Program?

To execute Java code, you must use a fully qualified name. When a name is fully qualified, it refers to a class name with an entire package structure. Packages in Java, To run Java code, use the syntax listed below.

Syntax:

java completePackageName.className

Now run the Java code.
To Run:   java com.scientecheasy.java.corejava.Example

Output: 

 My first basic example.

How to Access A Package?

It becomes necessary to access a package inside another Java program file in practically all real-world projects (or as soon as you progress past Java’s foundational concepts).

The import keyword is used to include specific package files in the running Java program. Packages in JAVA, There are primarily three methods for accessing a package’s files.

Using packageName (dot) *

package packageB;  

import packageA.*;  

class B{  

  public static void main(String args[]){ 

    // A class is present inside packageA

   A obj = new A();   

  }  

} 

Advantages of Packages in Java

Reusability: 

We can put
the shared code in a shared folder so that everyone can access it and use it as needed.

Organized: 

Additionally, it aids in file organization for our project.

Access Protection: 

Access security is provided by a package. It can be applied to control visibility. Packages in java, It is possible to define the class’s members so that only components belonging to that package can see them.

Maintenance: 

For effective maintenance, Java packages are utilized. Any developer who has recently joined a company can readily access the necessary files.

Key points:

1. When importing another package, the package declaration statement must come first, then the package import statement.
2. Although a class may only have one package statement, it may contain several import package statements.
3. After the package declaration and before the class statement, import can be written numerous times.
4. The last file name must be the class name with a semicolon, and you must declare the package with the root folder name (no subdirectory names).
5. It is true that RAM gets allocated when you import. Just the path to the file is provided.

Conclusion

Classes, interfaces, and sub-packages are examples of comparable Java files that are grouped together in packages in Java (don’t forget the analogy of storing data inside of a laptop). Java packages come in two varieties: built-in packages and user-defined packages. Packages in Java, Packages have a number of benefits, including the ability to avoid name collision errors, ease of management, and security.

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