Core Java Quiz ( Advanced ) - All Questions

This advanced Core Java quiz is designed for experienced Java developers preparing for senior-level interviews. It covers JVM internals, memory management, concurrency, collections internals, design principles, performance tuning, and real-world Java problem-solving scenarios.

Question 1: What is the primary responsibility of the ClassLoader in Java?

Execute bytecode
Load classes into JVM memory
Manage heap memory
Optimize bytecode

Explanation: ClassLoader loads class bytecode into JVM memory.

Question 2: Which memory area stores class metadata in modern JVMs?

Heap
Stack
Metaspace
Code Cache

Explanation: Metaspace stores class metadata in Java 8+.

Question 3: What was replaced by Metaspace in Java 8?

Heap
Stack
PermGen
Eden Space

Explanation: PermGen was replaced by Metaspace.

Question 4: Which GC algorithm is optimized for low-latency applications?

Serial GC
Parallel GC
G1 GC
Mark and Sweep

Explanation: G1 GC aims to reduce pause times.

Question 5: What does the 'volatile' keyword guarantee?

Atomicity
Thread safety
Visibility across threads
Mutual exclusion

Explanation: volatile guarantees visibility of changes across threads.

Question 6: Which Java construct provides mutual exclusion?

volatile
final
synchronized
transient

Explanation: synchronized ensures mutual exclusion.

Question 7: Why is double-checked locking used?

Reduce memory usage
Ensure thread safety with performance
Avoid deadlocks
Improve GC

Explanation: It minimizes synchronization overhead while maintaining safety.

Question 8: Which collection is not thread-safe by default?

Hashtable
Vector
ConcurrentHashMap
ArrayList

Explanation: ArrayList is not synchronized.

Question 9: What is the main difference between HashMap and ConcurrentHashMap?

Memory usage
Thread safety and locking strategy
Key uniqueness
Iteration order

Explanation: ConcurrentHashMap supports concurrent access with fine-grained locking.

Question 10: Why is HashMap not thread-safe?

Allows null keys
Uses hashing
No synchronization during modification
Uses equals method

Explanation: Lack of synchronization causes race conditions.

Question 11: What can happen if HashMap is modified concurrently?

Compilation error
Deadlock
Infinite loop during rehashing
Automatic synchronization

Explanation: Concurrent modification may cause infinite loops.

Question 12: Which interface supports functional programming in Java?

Serializable
Runnable
FunctionalInterface
Comparable

Explanation: @FunctionalInterface enables lambda expressions.

Question 13: Which Java feature enables lambda expressions?

Generics
Annotations
Functional interfaces
Reflection

Explanation: Lambdas work with functional interfaces.

Question 14: What is the purpose of the Stream API?

Thread management
Functional data processing
File handling
Memory allocation

Explanation: Streams support functional-style data processing.

Question 15: Which Stream operation transforms data?

filter()
forEach()
map()
collect()

Explanation: map() transforms elements.

Question 16: Which Stream operation is terminal?

map()
filter()
sorted()
collect()

Explanation: collect() is a terminal operation.

Question 17: What is the fork/join framework used for?

Thread pooling
Parallel task execution
Asynchronous IO
Memory sharing

Explanation: Fork/Join supports parallelism.

Question 18: Which exception indicates class loading failure?

IOException
ClassNotFoundException
NoClassDefFoundError
InstantiationException

Explanation: ClassNotFoundException occurs during dynamic loading.

Question 19: Difference between Error and Exception?

Errors are recoverable
Exceptions are unchecked
Errors are serious system issues
Exceptions stop JVM

Explanation: Errors represent serious system problems.

Question 20: Which design principle does Java strongly follow?

DRY
SOLID
YAGNI
KISS

Explanation: Java design aligns strongly with SOLID principles.

Question 21: What is immutability mainly used for?

Memory optimization
Thread safety and predictability
Serialization
Garbage collection

Explanation: Immutable objects are inherently thread-safe.

Question 22: Why are wrapper classes immutable?

Performance
Security and caching
Simpler syntax
Serialization

Explanation: Immutability allows caching and thread safety.

Question 23: Which Java feature supports lazy initialization?

Static blocks
Inner static helper class
Constructor chaining
Reflection

Explanation: Static inner classes enable lazy loading.

Question 24: What is escape analysis used for?

Security checks
Optimizing object allocation
Exception handling
Thread management

Explanation: Escape analysis optimizes memory allocation.

Question 25: Which JVM optimization eliminates object allocation?

Inlining
Scalar replacement
Loop unrolling
Dead code elimination

Explanation: Scalar replacement avoids heap allocation.

Question 26: What does JIT compiler do?

Compile source code
Interpret bytecode
Optimize bytecode at runtime
Manage memory

Explanation: JIT compiles bytecode into native code.

Question 27: Why is final keyword important for performance?

Prevents GC
Enables JVM optimizations
Reduces memory usage
Improves IO speed

Explanation: final allows aggressive JVM optimizations.

Question 28: Which reference type helps prevent memory leaks?

Strong
Weak
Soft
Phantom

Explanation: Weak references allow GC cleanup.

Question 29: Which collection uses red-black tree internally?

HashMap
ArrayList
TreeMap
LinkedList

Explanation: TreeMap is based on red-black tree.

Question 30: Why is equals() contract important?

Serialization
Hash-based collections correctness
Memory allocation
Thread safety

Explanation: equals() affects HashMap and HashSet behavior.

Question 31: What must be overridden with equals()?

toString()
compareTo()
hashCode()
clone()

Explanation: hashCode must align with equals.

Question 32: Which concurrency issue causes inconsistent data?

Deadlock
Starvation
Race condition
Livelock

Explanation: Race conditions cause inconsistent results.

Question 33: What is livelock?

Threads blocked forever
Threads active but not progressing
CPU idle state
Dead JVM

Explanation: Threads keep responding without progress.

Question 34: Which Executor service is best for CPU-bound tasks?

CachedThreadPool
SingleThreadExecutor
FixedThreadPool
ScheduledExecutor

Explanation: FixedThreadPool suits CPU-bound workloads.

Question 35: Why should checked exceptions be used carefully?

They reduce performance
They increase tight coupling
They break compilation
They use more memory

Explanation: Checked exceptions increase coupling.

Question 36: What is the purpose of Serializable?

Thread safety
Object persistence
Cloning objects
Security

Explanation: Serializable enables object persistence.

Question 37: Why is Externalizable rarely used?

Complex implementation
Performance issues
Security risks
Deprecated API

Explanation: It requires manual serialization logic.

Question 38: Which pattern ensures only one instance exists?

Factory
Builder
Singleton
Prototype

Explanation: Singleton restricts instantiation.

Question 39: Which Singleton implementation is thread-safe and lazy?

Eager initialization
Enum singleton
Synchronized method
Double-checked locking

Explanation: Double-checked locking is lazy and efficient.

Question 40: What is the main drawback of Singleton?

High memory usage
Difficult unit testing
Slow performance
Complex syntax

Explanation: Singletons hinder testability.

Question 41: Which principle suggests depending on abstractions?

Single Responsibility
Open-Closed
Dependency Inversion
Liskov Substitution

Explanation: DIP encourages abstraction-based design.

Question 42: What is the biggest advantage of interfaces over abstract classes?

Faster execution
Multiple inheritance support
State management
Better encapsulation

Explanation: Interfaces support multiple inheritance.

Question 43: Why should reflection be used cautiously?

Syntax complexity
Performance and security risks
Compilation errors
Memory leaks

Explanation: Reflection impacts performance and security.

Question 44: What is the primary goal of Core Java mastery?

Framework usage
Writing scalable and maintainable Java systems
Frontend development
Database optimization

Explanation: Core Java builds strong, scalable foundations.

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Core Java Quiz ( Advanced )

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