Essential Java Interview Questions for Beginners Quiz

Boost your Java basics and get interview-ready with these easy, must-know questions covering core Java features, OOP concepts, data structures, and exception handling.

1. Java Core Feature Identification

   Which of the following is NOT a main feature of Java?

   1. Object-Oriented
   2. Robust
   3. Platform Dependent
   4. Multithreaded

   Explanation: Java is known for being platform independent, not platform dependent. Object-Oriented, Multithreaded, and Robust are listed as main features in the context, making Platform Dependent incorrect.

2. JDK, JRE, and JVM Comparison

   What does the JDK (Java Development Kit) include that the JRE (Java Runtime Environment) does NOT?

   1. Java Virtual Machine
   2. Development tools and compiler
   3. Bytecode interpreter
   4. Class libraries

   Explanation: JDK includes all of JRE plus development tools and a compiler, which JRE does not provide. The JVM and class libraries are parts of JRE, and the bytecode interpreter is handled by the JVM.

3. Comparing == and .equals()

   In Java, what does the == operator do when used with objects?

   1. Copies values between objects
   2. Sorts the objects
   3. Compares memory addresses
   4. Compares string content

   Explanation: == checks if two references point to the same memory address. Comparing string content should use .equals(). Sorting and copying values are unrelated to ==.

4. Understanding OOPs Pillars

   Which OOP concept involves hiding implementation details and showing only functionality?

   1. Abstraction
   2. Encapsulation
   3. Polymorphism
   4. Inheritance

   Explanation: Abstraction is about hiding implementation details and showing only what is necessary. Inheritance deals with property transfer, polymorphism with varied behavior, and encapsulation with data wrapping.

5. ArrayList vs LinkedList Use Cases

   According to the context, when is LinkedList preferred over ArrayList?

   1. For frequent insertions and deletions
   2. For fast searching by index
   3. When using hash functions
   4. For slower deletion

   Explanation: LinkedList is best for frequent insertions and deletions. ArrayList is better for fast searching by index. LinkedList does not specifically use hash functions, and it is not preferred for slow operations.

6. Understanding throw vs throws

   In Java, what is the use of the 'throws' keyword?

   1. Declare exceptions in a method signature
   2. Trigger an exception inside a method
   3. Close resources after exceptions
   4. Ignore exception handling

   Explanation: 'throws' is used in method declarations to state what exceptions might be thrown. 'throw' triggers an exception inside a method. Closing resources and ignoring exceptions are not related to 'throws'.

7. Keywords: final, finally, finalize()

   Which term refers to a method called before object destruction by the garbage collector?

   1. finalize()
   2. finish
   3. finally
   4. final

   Explanation: 'finalize()' is called by the garbage collector before destroying an object. 'final' is a keyword for constants or inheritance control, 'finally' is a block in exception handling, and 'finish' is not a Java term.

8. Multithreading Benefits

   What is a key advantage of using multithreading in Java applications?

   1. Enforces single-tasking
   2. Reduces code size
   3. Maximizes CPU utilization
   4. Prevents all exceptions

   Explanation: Multithreading allows multiple tasks to run concurrently, maximizing CPU utilization. It does not directly reduce code size, prevent all exceptions, or enforce single-tasking—in fact, it enables multitasking.

9. Abstract Class vs Interface

   What is true about an abstract class compared to an interface (Java 8+)?

   1. It cannot have variables
   2. It cannot have concrete methods
   3. It can have both abstract and concrete methods
   4. It cannot have constructors

   Explanation: Abstract classes can have both abstract and concrete methods, as well as constructors and variables. Interfaces (Java 8+) can't have constructors but can have static/default methods.

10. Checked vs Unchecked Exceptions

    Which exception must be handled at compile-time in Java?

    1. Checked Exception
    2. RuntimeException
    3. NullPointerException
    4. Unchecked Exception

    Explanation: Checked exceptions, like IOException, are checked at compile-time and must be handled. Unchecked exceptions (including RuntimeException and NullPointerException) occur at runtime and don't require explicit handling.