Last Updated : 12 Aug, 2025
Java is a high-level, object-oriented programming language used to build web apps, mobile applications, and enterprise software systems.
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Here is a simple Java program that prints "Hello World".
Java
// A Java program to print "Hello World"
public class Geeks {
public static void main(String args[])
{
System.out.println("Hello World");
}
}
Java Basics
Java basics form the foundation of your programming journey, covering essential concepts like syntax, data types, variables, loops, and conditionals. Mastering these fundamentals is key to building strong, error-free Java applications:
Java methods are reusable blocks of code that perform specific tasks and help organize your program. They improve code readability, reduce repetition, and make debugging easier:
Java arrays are containers that store multiple values of the same data type in a single variable. They provide an efficient way to manage and access collections of data using index-based positions:
Java Strings represent sequences of characters and are widely used in text processing. They are immutable, meaning once created, their values cannot be changed:
Java follows the Object-Oriented Programming (OOP) paradigm, which organizes code into classes and objects. Core OOP principles like inheritance, encapsulation, polymorphism, and abstraction make Java modular and scalable:
Java interfaces define a contract that classes must follow, specifying method signatures without implementations. They enable abstraction and support multiple inheritance in Java through a clean, structured approach:
Java Collections provide a framework for storing and manipulating groups of objects efficiently. It includes interfaces like List, Set, and Map, along with classes like ArrayList, HashSet, and HashMap:
ava Exception Handling is a mechanism to handle runtime errors, ensuring the program runs smoothly without crashing. It uses keywords like try, catch, throw, throws, and finally to manage exceptions:
Java Multithreading allows concurrent execution of two or more threads, enabling efficient CPU utilization and faster program performance. It is commonly used for tasks like parallel processing and responsive applications:
Java File Handling enables programs to create, read, write, and manipulate files stored on the system. It uses classes from the java.io and java.nio packages for efficient file operations:
Java Streams and Lambda Expressions simplify data processing by enabling functional-style operations on collections. Lambdas provide concise syntax for anonymous functions, while Streams allow efficient filtering, mapping, and reduction of data:
Java IO (Input/Output) provides a set of classes and streams to read and write data from various sources like files, consoles, and network connections. It is part of the java.io package and supports both byte and character streams:
Java Synchronization is used to control access to shared resources in multithreaded environments. It ensures that only one thread can access a critical section at a time, preventing data inconsistency:
Java Regex (Regular Expressions) allows pattern matching and text manipulation using the java.util.regex package. It is powerful for validating, searching, and replacing strings based on specific patterns:
Java Networking enables communication between devices over a network using classes from the java.net package. It supports protocols like TCP and UDP for building client-server applications and data exchange:
Java Memory Allocation refers to how memory is assigned to variables, objects, and classes during program execution. It involves stack and heap memory, with the JVM managing allocation and garbage collection automatically:
Prepare for Java interviews with these commonly asked questions, covering core concepts, OOP, collections, multithreading, exception handling, and frameworks like Spring and Hibernate:
Important LinksJava Practice
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