Ultimate Guide to Java Interview Questions
If you're preparing for a Java interview, mastering these questions will give you a strong foundation. This post covers all critical Java topics, from Core Java concepts to Advanced topics, including coding challenges. Let's dive in!
Core Java Basics
What are the key features of Java?
Explain the difference between JDK, JRE, and JVM.
What is the difference between == and .equals() in Java?
What is a Class and an Object in Java?
Explain the public static void main(String[] args) method.
What is the difference between String, StringBuilder, and StringBuffer?
What are access modifiers in Java? Describe their scope.
What is the difference between final, finally, and finalize?
OOP (Object-Oriented Programming)
What are the four pillars of OOP? Explain each with examples.
What is the difference between abstraction and encapsulation?
What is method overloading and method overriding?
What is the difference between an interface and an abstract class?
Can a class implement multiple interfaces? How?
What is constructor overloading? Provide an example.
What is the use of super and this keywords in Java?
Collections and Data Structures
What is the difference between ArrayList and LinkedList?
What is the difference between HashMap, LinkedHashMap, and TreeMap?
What is the significance of hashCode() and equals() in a HashMap?
What is the difference between Iterator and ListIterator?
Explain the fail-fast and fail-safe iterators in Java.
How does a HashMap work internally in Java?
What is the difference between Set, List, and Queue interfaces?
What is a ConcurrentHashMap and how is it different from HashMap?
Multithreading and Concurrency
What is the difference between a process and a thread?
How do you create threads in Java? Explain using Runnable and Thread.
What is the difference between synchronized method and block?
What is the difference between wait(), notify(), and notifyAll()?
What is the difference between Callable and Runnable?
What is the purpose of the volatile keyword?
What is a deadlock? How can you prevent deadlocks?
Explain the ThreadPoolExecutor and its benefits.
Exception Handling
What is the difference between checked and unchecked exceptions?
What is the purpose of the try, catch, and finally blocks?
What is the difference between throw and throws?
What is a custom exception? How do you create it?
What is the difference between Error and Exception?
What happens if an exception is thrown in a finally block?
Java 8+ Features
What are functional interfaces? Provide examples.
What is a lambda expression? How is it used in Java 8?
What is the Stream API in Java?
What is the difference between map() and flatMap() in Streams?
What are the default and static methods in interfaces?
What is the Optional class in Java?
What is the purpose of the forEach() method in Streams?
Memory Management
What is garbage collection in Java? How does it work?
What are strong, weak, soft, and phantom references?
What are the memory areas allocated by JVM?
How can you force garbage collection in Java?
What is the difference between stack and heap memory?
Advanced Java Topics
What is the difference between a Callable and Future?
Explain Java's memory model and its relationship with multithreading.
How does the Java Comparator interface work? How does it differ from Comparable?
What is reflection in Java?
What is the difference between a Proxy and a Reflection API?
What are Design Patterns? Explain Singleton and Factory patterns.
What is the Java NIO package and how does it differ from IO?
What is Serialization and Deserialization in Java?
Common Coding Questions
Write a program to check if a string is a palindrome.
Write a program to find the second-largest element in an array.
Write a program to reverse a linked list.
Write a program to implement a thread-safe Singleton class.
Write a program to find the frequency of characters in a string.
Write a program to demonstrate deadlock and resolve it.
Write a program to check if two strings are anagrams.
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