Java Programming — MCQ Practice Questions & Answers

Question 1

What is the output of the following code? class A { int x = 10; } class B extends A { int x = 20; } public class Test { public static void main(String[] args) { A obj = new B(); System.out.println(obj.x); } }

Accepted Answer

Correct answer: A. 10 — Variable overriding doesn't work in Java like method overriding. obj.x accesses the variable from reference type A, which has value 10.

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B. 20

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C. Compilation Error

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D. Runtime Error

Question 2

Which of the following statements about abstract classes is TRUE?

Accepted Answer

Correct answer: C. Abstract classes can have abstract methods and concrete methods — Abstract classes can contain both abstract methods (without implementation) and concrete methods (with implementation). They cannot be instantiated directly.

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A. Abstract classes can be instantiated

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B. Abstract classes cannot have concrete methods

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D. Abstract classes must extend another abstract class

Question 3

What will happen when you try to instantiate an interface in Java?

Accepted Answer

Correct answer: C. It will cause a compilation error — Interfaces cannot be instantiated directly. You must create a class that implements the interface. Attempting this causes a compilation error.

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A. It will create an instance successfully

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B. It will throw a RuntimeException

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D. It depends on the JVM version

Question 4

Which of the following best describes encapsulation?

Accepted Answer

Correct answer: A. Hiding implementation details and providing controlled access through methods — Encapsulation involves bundling data (variables) and methods, hiding implementation details, and providing public methods for access. It protects data integrity.

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B. Creating objects from classes

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C. Inheriting properties from parent class

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D. Using multiple methods with the same name

Question 5

Which of the following is true about method overloading?

Accepted Answer

Correct answer: B. Methods must have same name but different parameters — Method overloading requires methods to have the same name but different parameter lists (number, type, or order of parameters). Return type alone is insufficient.

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A. Methods must have different return types

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C. Methods must be in different classes

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D. Only constructors can be overloaded

Question 6

What is the correct way to prevent a class from being inherited in Java?

Accepted Answer

Correct answer: B. Mark it as 'final' — The 'final' keyword prevents a class from being extended. String, Integer, and other wrapper classes are marked final for security and immutability.

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A. Mark it as 'private'

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C. Mark it as 'abstract'

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D. Mark it as 'static'

Question 7

What is the output? class A { A() { System.out.println("A"); } } class B extends A { B() { super(); System.out.println("B"); } } public class Test { public static void main(String[] args) { new B(); } }

Accepted Answer

Correct answer: B. A then B — super() calls parent constructor first. Parent constructor A prints 'A', then child constructor B prints 'B'.

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A. B then A

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C. Only B

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D. Compilation Error

Question 8

Which of the following statements about 'instanceof' operator is correct?

Accepted Answer

Correct answer: B. It checks if an object is an instance of a class or interface — The 'instanceof' operator checks whether an object is an instance of a specific class or implements a specific interface.

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A. It checks if an object is created from a class

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C. It checks if a variable is static

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D. It converts object type

Java Programming - MCQ Practice Questions