Java Packages List

Why Use Packages

Using Packages in Java can be helpful in many ways:-

• Using packages in Java can aid in Data Encapsulation or Data Hiding.
• Using packages in Java creates a new namespace so the names of your Class and interfaces won’t conflict with the type names in other packages.
• You can allow types within the Package to have unrestricted access to one another yet still restrict access for types outside the Package.

All Packages

java.util Package

The java.util package contains the collection framework, legacy collection classes, event model, date and time facilities, and miscellaneous utility classes like string tokenizer, a random-number generator, and a bit array.

Java directly depends on several classes in this package

1. The HashTable class for implementing hashtables
2. Enumeration interface for iterating through a collection of elements
3. StringTokenizer class for parsing strings into distinct tokens
4. The Collection Framework contains inbuilt implementations of various data structures and algorithms.
    

Consider the below example of using the ArrayList class of the Collection Framework inside the java.util Package and Calendar class.

• Java

Java

import java.util.ArrayList;
import java.util.Calendar;

public class Demo {
	public static void main(String[] args) { 
		Calendar c = Calendar.getInstance();
		// Demonstration  of Calendar's get()method

		System.out.println("Current Calendar's Year: " + c.get(Calendar.YEAR));        
		System.out.println("Current Calendar's Day: " + c.get(Calendar.DATE));           

		// Demonstration of ArrayList class         

		ArrayList<String> list = new ArrayList<String>();         
		list.add("Java Packages List");         
		list.add("Coding Ninjas");         
		System.out.println(list);   
	}
}

You can also try this code with Online Java Compiler

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The output of the above program is:

Current Calendar's Year: 2021Current Calendar's Day: 11[Java Packages List, Coding Ninjas]

There are a lot of useful classes, methods, and interfaces in this package. Do check out the official documentation for more details.

There are a lot of useful classes, methods, and interfaces in this package. Do check out the official documentation for more details.

You can also check about Java Tokens here.

java.lang Package

Among the in-built Java Packages, the java.lang package provides classes that are fundamental to the design of the Java programming language. The most important Class in this Package is the Object class, which is the root of the class hierarchy and Class whose instances represent the classes at run time.

Furthermore, wrapper classes Boolean, Character, Integer, Float, and Double are also present in this Package.

This Package is automatically imported to each of the Java programs. Some of the essential Java classes and interfaces present in the Java.lang package are listed below:-

There are a lot of classes and interfaces in the Java.lang package. Do check out the official documentation for more details.

Consider the below example that uses the methods defined inside Math and Integer classes of java.lang package

• Java

Java

public class Demo  {
	public static void main(String[] args) {
		System.out.println(“Exploring Java packages list”); 
		int a = 60, b = 80;                  // Using methods defined inside Math class of Java
		int sum = Math.addExact(a, b);
		int multiply = Math.multiplyExact(a, b);
		System.out.println("Sum is: " + sum + " and multiplication is: " + multiply);               
		// Using methods defined inside Integer Wrapper class of Java

		int c = 100;                        // Use to convert an integer to string

		System.out.println("Using toString(c): " + Integer.toString(c));
		// Use to convert an integer to Binary String

		System.out.println("Using toBinaryString(c): " + Integer.toBinaryString(c));  
	}
}

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The output of the above program is:-

Exploring Java Packages ListSum is: 140 and multiplication is: 4800Using toString(c): 100Using toBinaryString(c): 1100100

java.io Package

This Package is one of the fundamental packages in the Java packages list. It provides classes and interfaces for handling input and output operations using data streams, serialization, and the file system. In Java, all the fundamental input and output operations are based on streams. A stream is a conceptually endless stream of data from InputStream or a Reader to OutputStream of a Writer.

Some of the essential Java classes and interfaces present in the java.io Package are listed below.

Source: Documentation

Exception classes of the java.io Package, Source Documentation

Consider the following program that uses FileOutputStream class of the java.io package to write a primitive value and a string to a file at the location specified. If the file is not present in the specified location, a new file will be created.

• Java

Java

import java.io.FileOutputStream;
public class Demo {
	public static void main(String[] args) {
		System.out.println("Exploring Java Packages List");
		try {
			FileOutputStream fout = new FileOutputStream("/workspaces/Demo-Web/Java/newfile.txt");
			// writing specified byte to the output stream

			fout.write(65);                                          // Writing String
			String str = “Coding Ninjas”;                   // Converting string to byte array
			byte[] arr = str.getBytes();
			fout.write(arr);                                         // Closing the FileOutputStream object
			fout.close();
			System.out.println("Successfully added ....");
		}
		catch(Exception e) {
			System.out.println("Exception Occured");
			System.out.println(e);
		}
	}
}

You can also try this code with Online Java Compiler

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The output of the above program is:

Exploring Java Packages ListSuccessfully added ….

Try and compile it on java compiler. The file newFile.txt will contain the following content ACoding Ninjas

For more information regarding methods do check out the official documentation.

java.awt Package

Java is a rich language in terms of in-built Java Packages. The java awt or Abstract Window Toolkit package contains classes and interfaces used to develop graphical user interfaces. The root of all AWT components is the Component class

Hierarchy of classes in Java.awt package

Some of the essential classes and interfaces in Java.awt Package is enlisted below:

1. AlphaComposite
2. Button
3. Canvas
4. CardLayout
5. Container
6. Dialog

You can study more about all the classes, interfaces, and methods in Java.awt Package in the official documentation.

There are 11 more in-built java packages in the Java package list. They all provide really useful classes and built-in methods to make a programmer’s life easier. 

Java.time Package

The java.time package contains LocalDate, LocalTime, LocalDateTime, ZonedDateTime, Duration, and Time classes. It also allows date and time string parsing and formatting and advanced functions like leap seconds, time-based arithmetic, and the ISO calendar system.

Code:

• Java

Java

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.Duration;
public class DateTimeExample {
  public static void main(String[] args) {
     // Creating LocalDate object with the current date
     LocalDate currentDate = LocalDate.now();
     System.out.println("Current date: " + currentDate);
     // Creating LocalDateTime object with the current date and time
     LocalDateTime currentDateTime = LocalDateTime.now();
     System.out.println("Current date and time: " + currentDateTime);
     // Creating a Duration object of 5 hours
     Duration fiveHours = Duration.ofHours(5);
     System.out.println("Duration of 5 hours: " + fiveHours);
  }
}

You can also try this code with Online Java Compiler

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Output: 

Current date: 2023-03-25
Current date and time: 2023-03-25T05:16:05.509648
Duration of 5 hours: PT5H

Must Read: Java System Out Println and Hashcode Method in Java.

Java.sql Package

Java's java.sql package contains classes and interfaces for connecting to and modifying relational databases. It is used in Java database programming and offers a standard API for working with different types of databases. The following are some of the important classes and interfaces in the java.sql package:

• Connection: Represents a database relationship.
• Statement: Executes a SQL query.
• PreparedStatement: A SQL statement that has been precompiled and can be run numerous times with different parameters.
• CallableStatement: Runs a database stored function.
• ResultSet: This class represents the outcome of a query.
• SQLException: A database exception that happened while working with it.

Java.net Package

The java.net package contains networking methods in Java. It includes classes for dealing with various network protocols such as TCP, UDP, HTTP, and FTP.

The Java.net Package is divided into 2 parts, which are discussed below:

A Low-Level API that handles the following abstractions:

• Addresses are networking identifiers similar to IP numbers.
• Sockets are fundamental bidirectional data transmission mechanisms.
• Interfaces are used to define network interfaces.

A High-Level API that handles the following abstractions:

• URIs are short for Universal Resource Identifiers.
• URLs are short for Universal Resource Locators.
• Connections, which indicate links to the resources referenced by URLs.

Java.math Package

The java.math package is a built-in Java package that contains classes for conducting advanced mathematical operations such as arbitrary-precision arithmetic, numerical computation, and random number generation.

Some important Classes in Java.math: 

• BigDecimal: Signed decimal numbers with arbitrary accuracy that are immutable.
• BigInteger: Immutable integers with arbitrary accuracy.
• MathContext: Immutable objects that contain context settings for numerical operators, such as those implemented by the BigDecimal class.
• RoundingMode: RoundingMode defines the rounding behavior for numerical processes that can discard precision.

Java.text Package

The java.text package is a built-in Java package that offers classes for formatting and parsing text, as well as numbers, dates, and times. This package is useful in internationalization and localization apps that require text to be formatted or parsed based on locales, languages, or cultural tastes.
Some important classes in Java.text Package are:

• AttributedString: An AttributedString contains text as well as attribute information.
• ChoiceFormat: A ChoiceFormat enables you to associate a format with a range of numbers.
• Collator: The Collator class conducts locale-sensitive String comparison.
• DateFormat: DateFormat is an abstract class for date/time formatting subclasses that format and parses dates or times in a language-independent way.

Javax.xml Package

The javax.xml package, which is part of the Java API for XML Processing (JAXP), contains classes for dealing with XML data in Java. It contains XML parsing, generation, transformation, and validation classes.

Class of Javax.xml Package is:

• XMLConstants: Utility class containing constants representing fundamental XML values.

Must Read Conditional Statements in Java

Frequently Asked Questions

What are API packages in Java?

API packages in Java are pre-defined libraries, such as java.util or java.io, providing reusable classes and methods for various functionalities.

How many packages are there in Java API?

Java API includes hundreds of packages, with core ones like java.lang, java.util, java.io, and many others, grouped by functionality.

What is REST API in Java?

A REST API in Java allows applications to communicate over HTTP, adhering to REST principles, enabling CRUD operations with standard web methods like GET, POST, PUT, and DELETE.

Conclusion

This blog attempted to give an overview of Packages in Java. Predefined packages in Java, along with their classes and interfaces, were also introduced.

With this done, you can now switch to learn more about the Java programming language. 

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