1
What is Java? Easy
Java is a high-level, object-oriented programming language developed by Sun Microsystems (now Oracle). It is platform-independent due to the JVM (Java Virtual Machine).
- Compiled into bytecode
- Runs on JVM
- Write Once, Run Anywhere
2
What are the main features of Java? Easy
Key features of Java include:
- Object-Oriented
- Platform Independent
- Secure
- Robust
- Multithreaded
- High Performance (JIT compiler)
3
What is JVM? Easy
JVM (Java Virtual Machine) is responsible for executing Java bytecode. It provides platform independence and memory management.
4
What is JDK and JRE? Easy
JDK: Java Development Kit (compiler + tools)
JRE: Java Runtime Environment (JVM + libraries)
5
What is OOP? Easy
Object-Oriented Programming organizes code using objects and classes.
- Encapsulation
- Abstraction
- Inheritance
- Polymorphism
6
What is a class? Easy
A class is a blueprint for creating objects. It defines properties and behaviors.
7
What is an object? Easy
An object is an instance of a class containing state and behavior.
8
What is inheritance? Easy
Inheritance allows one class to acquire properties of another class using extends.
9
What is polymorphism? Easy
Polymorphism allows methods to behave differently based on context (method overloading & overriding).
10
What is encapsulation? Easy
Encapsulation wraps data and methods together using private variables and public getters/setters.
11
What is abstraction? Easy
Abstraction hides internal implementation details using abstract classes or interfaces.
12
What is method overloading? Easy
Same method name with different parameters in the same class.
13
What is method overriding? Easy
Subclass provides specific implementation of a method defined in parent class.
14
What is constructor? Easy
A constructor initializes object state and has same name as class.
15
What is static keyword? Easy
Static members belong to class rather than object.
16
What is final keyword? Easy
final prevents modification:
- Final variable → constant
- Final method → cannot override
- Final class → cannot inherit
17
What is interface? Easy
An interface defines abstract methods that classes must implement.
18
What is abstract class? Easy
An abstract class may contain abstract and concrete methods.
19
What is String in Java? Easy
String is immutable and stored in String pool.
20
Difference between == and equals()? Easy
== compares references.
equals() compares content.
21
What is ArrayList? Easy
ArrayList is a dynamic array implementation of List interface.
22
What is HashMap? Easy
HashMap stores key-value pairs and does not maintain order.
23
What is exception? Easy
An exception is an event that disrupts program flow.
24
Checked vs Unchecked Exception? Easy
Checked exceptions are compile-time checked.
Unchecked exceptions are runtime exceptions.
25
What is try-catch block? Easy
Used to handle exceptions in Java.
26
What is multithreading? Medium
Multithreading allows concurrent execution of two or more threads.
Improves CPU utilization.
27
What is Thread class? Medium
Thread class enables creation of threads.
28
Runnable vs Thread? Medium
Runnable is preferred because Java supports single inheritance.
29
What is synchronization? Medium
Synchronization prevents race condition using synchronized keyword.
30
What is deadlock? Medium
Deadlock occurs when two threads wait for each other’s resources.
31
What is garbage collection? Medium
Automatic memory management by JVM.
32
What is heap and stack? Medium
Heap stores objects. Stack stores method calls and local variables.
33
What is Comparable? Medium
Comparable interface is used for sorting custom objects.
34
What is Comparator? Medium
Comparator defines custom sorting logic.
35
What is serialization? Medium
Serialization converts object into byte stream.
36
What is transient keyword? Medium
Transient prevents variable from being serialized.
37
What is volatile keyword? Medium
Volatile ensures variable visibility across threads.
38
What is Optional class? Medium
Optional avoids NullPointerException.
39
What is Stream API? Medium
Stream API processes collections functionally.
40
What is lambda expression? Medium
Lambda provides concise way to implement functional interface.
41
What is functional interface? Medium
Interface with single abstract method.
42
What is default method in interface? Medium
Default method provides implementation inside interface.
43
What is Enum? Medium
Enum defines fixed set of constants.
44
What is reflection? Medium
Reflection allows inspecting classes at runtime.
45
What is class loader? Medium
Loads class files into JVM.
46
What is Spring Framework? Medium
Spring is enterprise Java framework for dependency injection and web apps.
47
What is REST API? Medium
REST is architectural style for building APIs.
48
What is Hibernate? Medium
Hibernate is ORM framework for Java.
49
What is JDBC? Medium
JDBC connects Java with databases.
50
What is SOLID principle? Medium
SOLID principles improve software design and maintainability.
51
Explain JVM architecture in detail. Hard
JVM consists of:
- Class Loader
- Runtime Data Areas
- Execution Engine
- Garbage Collector
52
What is Java Memory Model? Hard
Defines how threads interact through memory.
53
What is ConcurrentHashMap? Hard
Thread-safe version of HashMap.
54
What is ForkJoinPool? Hard
Framework for parallel execution using divide-and-conquer.
55
Explain double-checked locking. Hard
Optimized singleton implementation pattern.
56
What is immutability? Hard
Immutable objects cannot change after creation.
57
What is design pattern? Hard
Reusable solution to common design problems.
58
Explain Singleton pattern. Hard
Ensures only one instance of class exists.
59
What is Builder pattern? Hard
Separates construction of object from representation.
60
Explain Factory pattern. Hard
Factory pattern creates objects without exposing creation logic.
61
What is microservices architecture? Hard
Architecture style where application is built as collection of small services.
62
What is Docker in Java projects? Hard
Docker containers package Java app with dependencies.
63
Explain ThreadLocal. Hard
Provides thread-local variables.
64
What is CompletableFuture? Hard
Used for asynchronous programming in Java 8.
65
Explain Reactive Programming in Java. Hard
Asynchronous data stream processing using Project Reactor or RxJava.
66
What is JIT compiler? Hard
Just-In-Time compiler converts bytecode to native code for performance.
67
What is GraalVM? Hard
High-performance polyglot runtime for Java.
68
What is lock-free programming? Hard
Concurrency approach without explicit locks.
69
Explain distributed transactions. Hard
Transaction management across multiple services/databases.
70
How to scale Java application? Hard
Use load balancing, caching, clustering, containerization and microservices.
📊 Questions Breakdown
🟢 Easy
25
🟡 Medium
25
🔴 Hard
20
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