Java interview questions
Study 10 topics in order — from setup and basics to the questions interviewers actually ask. Answers include code, tables, and a short speaking tip.
Java Basics and Object-Oriented Programming (OOP)
Learn Java OOP core. Master variables, classes, inheritance, method overriding, interfaces, abstract classes,...
String, StringBuffer, and StringBuilder
Differentiate immutable String from mutable StringBuffer and StringBuilder. Learn performance, memory allocati...
Collections Framework (List, Set, Map)
Master Java collections. Differentiate ArrayList vs LinkedList, HashSet vs TreeSet, HashMap vs TreeMap, and so...
Java Exception Handling & Debugging
Understand Java exception hierarchies. Learn throw/throws declaration, checked vs unchecked exceptions, try-wi...
Java Generics & Type Safety
Write reusable, type-safe Java code. Learn generic classes, methods, wildcards, bounded parameters, and type e...
File Handling and I/O Operations
Read/write files in Java. Master standard streams, Reader/Writer classes, buffer filters, NIO file systems, an...
Multithreading and Concurrency in Java
Master concurrent Java execution. Learn Thread lifecycle, Runnable interface, thread pools, executor services,...
Java Database Connectivity (JDBC)
Master JDBC APIs. Learn connection setups, prepared statements, transaction commits, batch updates, and result...
Java Lambda Expressions & Streams (Java 8+)
Write clean functional Java. Master lambda shorthand, stream filters, collectors, map-reductions, and parallel...
Java Annotations, Reflection & Design Patterns
Use reflection to inspect classes at runtime. Learn built-in annotations, custom metadata, and common structur...