300+ Core Java Interview Questions & Answers

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Module 1 Java Overview
Java overview Interview Q&As
Unit 1 17 Java Overview Interview Q&As  - Preview
Unit 2 4 Java Compile-time Vs Run-time Interview Q&As  - Preview
Module 2 Java data types
Java data types interview Q&As on primitives, strings, memory allocation, autoboxing, etc
Unit 1 8 Java data types interview Q&As  - Preview
Unit 2 7 Java primitives & objects memory consumption Q&As  - Preview
Unit 3 4 Java autoboxing & unboxing interview Q&As  - Preview
Unit 4 12 Java String class Interview Q&As  - Preview
Module 3 Java modifiers, annotations, initializers & constructors
Java modifiers, initializers & constructors
Unit 1 6 Java Modifiers every interviewer seems to like  - Preview
Unit 2 10 Java initializers, constructors, regular methods and static factory methods Q&As
Unit 3 8 Java Annotations interview Q&As
Unit 4 4 Java annotation types & processing interview Q&As
Module 4 Java classes, interfaces & class loaders
Java classes, interfaces & class loaders
Unit 1 12 Java classes and interfaces interview Q&As
Unit 2 3 Abstract classes Vs interfaces interview Q&As
Unit 3 3 Java class loading interview Q&As to ascertain your depth of Java knowledge
Module 5 Java Objects Interview Q&As
Object class methods equals( ), hashCode( ), toString( ), wait( ) & notify( ), immutable objects, serializing, casting, and cloning
Unit 1 5 Java Object class methods interview Q&As  - Preview
Unit 2 3 Object wait( ) & notify( ) interview Q&As
Unit 3 7 Object equals Vs == and pass by reference Vs value interview Q&As
Unit 4 10 Java immutable objects interview Q&As
Unit 5 10 Java serialization, cloning, and casting interview Q&As
Module 6 OOP & FP
Programming paradigms OOP and FP
Unit 1 10 Java OOP Interview Q&As
Unit 2 5 Inheritance Vs Composition OOP Interview Q&As  - Preview
Unit 3 2 Polymorphism OOP Interview Q&As
Unit 4 8 OOP Design principles interview Q&As
Unit 5 5 OOP Vs FP, FP concepts & where to use FP Q&As  - Preview
Unit 6 19 Java Functional Programming (i.e. FP) interview Q&As
Unit 7 Java FP Lambda expressions by examples
Module 7 Generics & Java Collection Framework(JCF)
Generics & Java Collection Framework(JCF)
Unit 1 12 Java Generics Interview Q&As  - Preview
Unit 2 5 Java Generics Wildcards Interview Q&As
Unit 3 17 Java Collection Framework (JCF) interview Q&As
Unit 4 9 Java data structures interview Q&As
Unit 5 4 Sorting objects in a Collection interview Q&As
Unit 6 8 Java Map interface & Caching interview Q&As
Unit 7 Lambda expressions to work with Java 8 Collections
Module 8 Java multithreading
Java multi-threading interview questions & answers. These are interviewers favourite as even the so called experienced struggle with this topic.
Unit 1 17 Java multi-threading interview Q&As  - Preview
Unit 2 7 Java locks & synchronized keyword interview Q&As
Unit 3 9 blocking, scheduling & daemon threads interview Q&As
Unit 4 7 Java Executor framework Interview Q&As
Unit 5 ExecutorService Vs Fork/Join & Future Vs CompletableFuture Interview Q&As
Unit 6 7 Java ThreadLocal interview Q&As
Unit 7 Java Thread stop, resume, suspend & interrupt interview Q&As
Unit 8 12 Java multi-threading differences between X and Y Q&As
Unit 9 Java multi-threading 15 scenarios interview Q&As
Module 9 What is wrong with this multithread code?

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

Unit 1 5 Ways to debug Java thread-safety issues  - Preview
Unit 2 Heap Vs Stack, Thread safety & Synchronization  - Preview
Unit 3 Deep Vs Shallow comparison & multithreading
Unit 4 An excellent written test multithreading question - wait/notify
Unit 5 Multithreading & Locks
Unit 6 Java Collection & ConcurrentModificationException
Unit 7 HashMap & Race condition
Unit 8 ConcurrentHashMap & Atomic operations
Unit 9 JConsole for debugging deadlocks in Java
Unit 10 jvisualvm to debug deadlocks in Java
Module 10 Exceptions Handling
Java Exceptions Handling Interview Q&As
Unit 1 5 Java exception handling interview Q&As
Module 11 Java I/O & NIO
Java I/O & NIO Interview Q&As
Unit 1 15 Java old I/O and NIO (i.e. New I/O) interview Q&As
Unit 2 Java 8 way to reading files
Module 12 JVM
Java Virtual Machine (i.e. JVM) interview Q&As
Unit 1 11 JVM memory model and Atomicity, Visibility, and Ordering interview Q&As
Unit 2 8 Java Garbage Collection interview Q&As to ascertain your depth of Java knowledge
Unit 3 jvisualvm to sample Java heap memory
Unit 4 5 JMX and MBean interview Q&As
Module 13 What is new?
What is new in Java?
Unit 1 Java 7 features list
Unit 2 Java 8 features list
Module 14 Java code quality
Hire candidates who are passionate about writing quality code.
Unit 1 How will you go about improving on the following Java code?
Unit 2 How will you go about ensuring code quality in Java apps?
Unit 3 5 Java unit testing interview Q&As
Unit 4 Mocks, stubs, domain, and anemic objects interview Q&As
Unit 5 30+ Java Code Review Checklist Items
Module 15 Debugging Java applications

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

Unit 1 7 debugging Java interview questions & answers
Unit 2 Debugging "NoSuchMethodError" in Java
Unit 3 Debugging JAR hell issues in Java
Unit 4 Debugging Java version issues
Unit 5 Remote debugging in Java with Java Debug Wire Protocol (JDWP)
Unit 6 Debugging like a pro with eclipse IDE tutorial for Java developers
Module 16 Performance considerations & memory management
Performance and memory related issues are prevalent & pays to hire candidates with awareness & experience.
Unit 1 4 Java application performance considerations interview Q&As
Unit 2 8 Java memory management interview Q&As
Unit 3 jvisualvm to detect memory leak
Module 17 Design 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 1 12 Java design patterns interview Q&As
Unit 2 5 Java singleton design pattern interview Q&As
Unit 3 Java Proxy, Decorator, Adapter, Bridge, and Facade design patterns Interview Q&As
Unit 4 3 Flyweight design pattern Interview Q&As to improve memory usage & performance