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Java

Java is one of the most widely used programming languages in the world. It powers Android apps, enterprise backends, financial systems, cloud services, and more. This track takes you from complete beginner to production-ready Java developer — covering every keyword, API, design pattern, and deployment strategy used in real companies.

210+ Topics

12–16 weeks

6–35 LPA

Start Learning →View Roadmap

Getting Started

Introduction to Java

History, philosophy, WORA, JDK vs JRE vs JVM

Installation & Setup

Install JDK 21, configure PATH, JAVA_HOME

Your First Java Program

Hello World, main method, class structure

Compilation & Execution

javac, java, bytecode, JVM execution flow

IntelliJ IDEA, VS Code, Eclipse, keyboard shortcuts

Language Fundamentals

Variables & Declaration

Declaration, initialization, naming rules, var keyword

Primitive types, reference types, type sizes, overflow

final keyword, static final, naming conventions

Arithmetic, relational, logical, bitwise, ternary, instanceof

Widening, narrowing, explicit casting, loss of precision

All 50+ reserved keywords with explanations

Expressions & Statements

Expression types, statement kinds, blocks

Comments & Javadoc

Single-line, multi-line, Javadoc, documentation best practices

Control Flow

If / Else / Else If

Conditional branching, nested conditions, shortcircuit evaluation

Switch Statements

Classic switch, switch expressions (Java 14+), pattern matching switch (Java 21)

Classic for, enhanced for-each, index manipulation

While & Do-While

Pre-check, post-check loops, infinite loop prevention

Break & Continue

Loop control, labeled break, labeled continue

Pattern Matching

instanceof pattern matching (Java 16+), switch patterns (Java 21)

Strings & Arrays

String class, immutability, string pool, common methods

StringBuilder & StringBuffer

Mutable strings, performance, thread safety differences

String Methods Reference

substring, indexOf, replace, trim, split, join, format, strip

Declaration, initialization, multidimensional arrays, jagged arrays

Arrays Utility Class

sort, binarySearch, copyOf, fill, asList, stream

Variable arguments, syntax, use cases, pitfalls

Methods & Functions

Defining methods, return types, parameters, calling methods

Method Overloading

Compile-time polymorphism, rules, ambiguity, best practices

Base case, recursive case, call stack, tail recursion

Pass by Value vs Reference

How Java passes arguments, primitive vs object behavior

Static Methods & Fields

static keyword, class-level members, utility classes

Object-Oriented Programming

Classes & Objects

Blueprint vs instance, new keyword, memory allocation

Default, parameterized, copy constructors, constructor chaining

this & super Keywords

Current instance reference, parent class access, constructor delegation

Access modifiers, getters, setters, data hiding

extends keyword, single vs multilevel, method overriding

Compile-time vs runtime polymorphism, method dispatch, VTABLE

Abstract classes, abstract methods, design intent

Interface syntax, default methods, static methods, multiple implementation

Abstract Class vs Interface

Key differences, when to use which, comparison table

Access Modifiers

private, protected, public, package-private with scope diagrams

Static nested, inner classes, local classes, anonymous classes

Enum declaration, methods, constructors, EnumSet, EnumMap

Records (Java 14+)

Immutable data carriers, auto-generated methods, compact constructors

Sealed Classes (Java 17+)

sealed, permits, non-sealed keywords, algebraic data types

Generics

Introduction to Generics

Type safety, generic classes, generic methods, type erasure

Bounded Wildcards

Unbounded, upper-bounded extends, lower-bounded super

Generics with Collections

Generic lists, maps, sets, type inference with diamond operator

Exception Handling

Exception Basics

Throwable hierarchy, checked vs unchecked, Error vs Exception

Try-Catch-Finally

Syntax, multiple catch blocks, finally execution guarantees

Throwing exceptions, declaring in method signature, propagation

Custom Exceptions

Creating exception classes, best practices, when to create

Try-with-Resources

AutoCloseable, automatic cleanup, suppressed exceptions

Multi-Catch & Exception Chaining

Catching multiple types, exception cause wrapping

Collections Framework

Collections Framework Overview

Hierarchy, interfaces, implementations, choosing the right collection

Dynamic arrays, capacity, resizing, RandomAccess, performance

Doubly linked list, Deque interface, use cases, performance

Hash table backing, O(1) operations, hashCode/equals contract

Red-black tree, sorted order, NavigableSet, Comparator

Insertion order preservation, hash table + linked list

Buckets, hash collisions, treeification (Java 8), load factor, rehashing

HashMap Internals Deep Dive

Bucket indexing math, treeification threshold, load factor rehashing, HashDOS protection

Sorted keys, NavigableMap, floorKey, ceilingKey, headMap, tailMap

Insertion / access order, LRU cache implementation

Concurrent Collections

ConcurrentHashMap, CopyOnWriteArrayList, BlockingQueue, fail-safe iterators

Stack class, Queue interface, ArrayDeque, PriorityQueue

Collections Utility Class

sort, reverse, shuffle, min, max, frequency, disjoint, unmodifiable wrappers

Iterator, ListIterator, fail-fast, fail-safe, for-each internals

Functional Programming (Java 8+)

Lambda Expressions

Syntax, functional interface target typing, capturing variables

Functional Interfaces

Predicate, Function, Consumer, Supplier, BiFunction, UnaryOperator

Method References

Static, instance, arbitrary instance, constructor references

Stream creation, intermediate operations, terminal operations, lazy evaluation

Stream Operations Deep Dive

map, filter, reduce, collect, flatMap, distinct, sorted, peek, findAny

toList, toSet, toMap, groupingBy, partitioningBy, joining, counting

Null-safe patterns, map, flatMap, orElse, orElseGet, ifPresent

Parallel Streams

ForkJoinPool, thread safety, when to use, pitfalls

Concurrency & Multithreading

Thread class, Runnable, lifecycle states, daemon threads

Synchronization

synchronized keyword, intrinsic locks, monitor, race conditions

volatile Keyword

Visibility guarantee, happens-before, CPU cache flushing

Locks & ReentrantLock

Lock interface, ReentrantLock, fairness, tryLock, ReadWriteLock

AtomicInteger, AtomicLong, AtomicReference, CAS operations

ExecutorService & Thread Pools

ThreadPoolExecutor, fixed, cached, scheduled, single pools

Callable & Future

Returning values from threads, Future.get, timeout, cancellation

CompletableFuture

Async composition, thenApply, thenCompose, allOf, anyOf, exceptionally

ForkJoin Framework

Divide and conquer, RecursiveTask, RecursiveAction, work-stealing

Virtual Threads (Java 21)

Project Loom, lightweight threads, carrier threads, structured concurrency

Deadlock, Livelock & Starvation

Coffman conditions, detection, prevention, avoidance strategies

Thread-Safe Design Patterns

Immutability, ThreadLocal, Producer-Consumer, double-checked locking

File I/O & Serialization

File I/O Basics

File class, FileInputStream, FileOutputStream, Reader, Writer

BufferedReader, BufferedWriter, performance benefits

Paths, Files, Channels, Buffers, non-blocking I/O, WatchService

Serializable interface, ObjectOutputStream, transient, serialVersionUID

Jackson, Gson, ObjectMapper, custom serializers, JsonNode

JVM Internals

JVM Architecture

ClassLoader, Runtime Data Areas, Execution Engine overview

JVM Memory Model

Heap, Stack, Metaspace, Method Area, PC Register, happens-before

Heap Generations & GC

Young Gen, Eden, Survivor, Old Gen, Minor GC, Major GC, Full GC

Garbage Collection Algorithms

Serial, Parallel, G1, ZGC, Shenandoah — tuning and trade-offs

JIT Compilation

C1/C2 compilers, hotspot detection, deoptimization, AOT

Bootstrap, Extension, Application loaders, delegation model

Performance & Debugging

Profiling Java Apps

JProfiler, VisualVM, JConsole, async-profiler, flame graphs

Heap Dumps & Thread Dumps

jmap, jcmd, Eclipse MAT, analyzing OOM errors

JVM Flags & Tuning

-Xms, -Xmx, -XX flags, GC logging, heap size tuning

Common causes, static references, unclosed resources, listener leaks

Benchmarking with JMH

Java Microbenchmark Harness, setup, avoiding JVM warm-up pitfalls

Spring Boot & Enterprise

Spring Framework Intro

IoC, DI, ApplicationContext, Spring vs Spring Boot

Spring Boot Setup

start.spring.io, pom.xml, auto-configuration, starters

Dependency Injection

Constructor injection, field injection, @Autowired, @Bean, @Component

Spring MVC & REST

@RestController, @GetMapping, @PostMapping, @RequestBody, @PathVariable

Spring Data JPA

JpaRepository, JPQL, N+1 problem, fetch types, custom queries

Spring Security

SecurityFilterChain, JWT, OAuth2, CSRF, role-based access

@Valid, @NotNull, @Size, @Email, BindingResult, custom validators

@Transactional, isolation levels, propagation, rollback rules

Testing Spring Apps

@SpringBootTest, MockMvc, Testcontainers, @MockBean, integration tests

Testing

@Test, @BeforeEach, @AfterEach, @ParameterizedTest, assertions

Mock, stub, verify, @Mock, @InjectMocks, ArgumentCaptor

Red-Green-Refactor cycle, writing tests first, coverage

Build Tools & Ecosystem

pom.xml, lifecycle phases, plugins, dependency management, repositories

build.gradle, Kotlin DSL, tasks, incremental builds, multi-project builds

Java Modules (JPMS)

module-info.java, exports, requires, encapsulation at package level

Design Patterns

Creational Patterns

Singleton, Factory, Abstract Factory, Builder, Prototype

Structural Patterns

Adapter, Bridge, Composite, Decorator, Facade, Flyweight, Proxy

Behavioral Patterns

Strategy, Observer, Command, Iterator, Template Method, Chain of Responsibility

SOLID Principles

SRP, OCP, LSP, ISP, DIP with Java code examples

Clean Architecture

Layers, dependency rule, use cases, entities, adapters

Interview Preparation

Beginner Interview Questions

Top 50 Java basics questions asked in freshers rounds

Advanced Interview Questions

JVM, concurrency, collections internals — senior engineer rounds

Coding Round Patterns

Array, string, tree, graph patterns commonly asked in Java interviews

Company-Specific Questions

Java questions asked at Google, Amazon, Microsoft, TCS, Infosys

300+ multiple choice questions with explanations for placement tests

Java Cheatsheet

Quick reference for syntax, keywords, collections complexity, streams

Best Practices & Anti-Patterns

Java Best Practices

Effective Java principles, clean code, naming, error handling

Common Mistakes

NullPointerException, == vs equals, float precision, ConcurrentModificationException

Performance Tips

String concatenation, autoboxing, stream misuse, collection sizing

SQL injection, XSS, secure hashing, OWASP Java guidelines

Companies Using Java

GoogleAmazonMicrosoftOracleNetflixUberLinkedInFlipkartTCSInfosys