300+ Core Java Interview Questions & Answers

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Module 1Java Overview
Java overview Interview Q&As
Unit 117 Java Overview Interview Q&As  - Preview
Unit 24 Java Compile time Vs Runtime Interview Q&As  - Preview
Module 2Java data types
Java data types interview Q&As
Unit 18 Java data types interview Q&As  - Preview
Unit 27 Java primitives & objects memory consumption Q&As
Unit 34 Java autoboxing & unboxing interview Q&As
Unit 412 Java String class Interview Q&As  - Preview
Module 3Java modifiers, annotations, initializers & constructors
Java modifiers, initializers & constructors
Unit 16 Java Modifiers every interviewer seems to like  - Preview
Unit 210 Java initializers, constructors, regular methods and static factory methods Q&As
Unit 38 Java Annotations interview Q&As
Unit 44 Java annotation types & processing interview Q&As
Module 4Java classes, interfaces & class loaders
Java classes, interfaces & class loaders
Unit 112 Java classes and interfaces interview Q&As
Unit 23 Abstract classes Vs interfaces interview Q&As
Unit 33 Java class loading interview Q&As to ascertain your depth of Java knowledge
Module 5Java Objects Interview Q&As
Object class methods.
Unit 15 Java Object class methods interview Q&As  - Preview
Unit 23 Object wait( ) & notify( ) interview Q&As
Unit 37 Object equals Vs == and pass by reference Vs value interview Q&As
Unit 410 Java immutable objects interview Q&As
Unit 510 Java serialization, cloning, and casting interview Q&As
Module 6OOP & FP
Programming paradigms OOP and FP
Unit 110 Java OOP Interview Q&As
Unit 25 Inheritance Vs Composition OOP Interview Q&As
Unit 32 Polymorphism OOP Interview Q&As
Unit 48 OOP Design principles interview Q&As
Unit 55 OOP Vs FP, FP concepts & where to use FP Q&As
Unit 619 Java Functional Programming (i.e. FP) interview Q&As
Unit 7Java FP Lambda expressions by examples
Module 7Generics & Java Collection Framework(JCF)
Generics & Java Collection Framework(JCF)
Unit 112 Java Generics Interview Q&As  - Preview
Unit 25 Java Generics Wildcards Interview Q&As
Unit 317 Java Collection Framework (JCF) interview Q&As
Unit 49 Java data structures interview Q&As
Unit 54 Sorting objects in a Collection interview Q&As
Unit 68 Java Map interface & Caching interview Q&As
Unit 7Lambda expressions to work with Java 8 Collections
Module 8Java multithreading
Java multi threading interview Q&As
Unit 117 Java multi-threading interview Q&As  - Preview
Unit 27 Java locks & synchronized keyword interview Q&As
Unit 39 blocking, scheduling & daemon threads interview Q&As
Unit 47 Java Executor framework Interview Q&As
Unit 5ExecutorService Vs Fork/Join & Future Vs CompletableFuture Interview Q&As
Unit 67 Java ThreadLocal interview Q&As
Unit 7Java Thread stop, resume, suspend & interrupt interview Q&As
Unit 812 Java multi-threading differences between X and Y Q&As
Unit 9Java multi-threading 15 scenarios interview Q&As
Module 9What is wrong with this multithread code?

Often interviewers test your ability to write multithreaded code & diagnose multi-threading issues

Unit 15 Ways to debug Java thread-safety issues  - Preview
Unit 2Heap Vs Stack, Thread safety & Synchronization  - Preview
Unit 3Deep Vs Shallow comparison & multithreading
Unit 4An excellent written test multithreading question - wait/notify
Unit 5Multithreading & Locks
Unit 6Java Collection & ConcurrentModificationException
Unit 7HashMap & Race condition
Unit 8ConcurrentHashMap & Atomic operations
Unit 9JConsole for debugging deadlocks in Java
Unit 10jvisualvm to debug deadlocks in Java
Module 10Exceptions Handling
Java Exceptions Handling Interview Q&As
Unit 15 Java exception handling interview Q&As
Module 11Java I/O & NIO
Java I/O & NIO Interview Q&As
Unit 115 Java old I/O and NIO (i.e. New I/O) interview Q&As
Unit 2Java 8 way to reading files
Module 12JVM
Java Virtual Machine (i.e. JVM) interview Q&As
Unit 111 JVM memory model and Atomicity, Visibility, and Ordering interview Q&As
Unit 28 Java Garbage Collection interview Q&As to ascertain your depth of Java knowledge
Unit 3jvisualvm to sample Java heap memory
Unit 45 JMX and MBean interview Q&As
Module 13What is new?
What is new in Java?
Unit 1Java 7 features list
Unit 2Java 8 features list
Module 14Java code quality
Hire candidates who are passionate about writing quality code.
Unit 1How will you go about improving on the following Java code?
Unit 2How will you go about ensuring code quality in Java apps?
Unit 35 Java unit testing interview Q&As
Unit 4Mocks, stubs, domain, and anemic objects interview Q&As
Unit 530+ Java Code Review Checklist Items
Module 15Debugging Java applications

It requires right know-hows & experience to debug Java applications

Unit 17 debugging Java interview questions & answers
Unit 2Debugging "NoSuchMethodError" in Java
Unit 3Debugging JAR hell issues in Java
Unit 4Debugging Java version issues
Unit 5Remote debugging in Java with Java Debug Wire Protocol (JDWP)
Unit 6Debugging like a pro with eclipse IDE tutorial for Java developers
Module 16Performance considerations & memory management
Performance and memory related issues are prevalent & pays to hire candidates with awareness & experience.
Unit 14 Java application performance considerations interview Q&As
Unit 28 Java memory management interview Q&As
Unit 3jvisualvm to detect memory leak
Module 17Design Patterns Interview Q&As
Design patterns are popular in job interviews. If you are are beginner, some level of awareness and experience can impress the interviewers.
Unit 112 Java design patterns interview Q&As
Unit 25 Java singleton design pattern interview Q&As
Unit 3Java Proxy, Decorator, Adapter, Bridge, and Facade design patterns Interview Q&As
Unit 43 Flyweight design pattern Interview Q&As to improve memory usage & performance