Java Programming Questions & Answers

Q.231 Easy OOP in Java

Which of the following correctly describes the 'this' keyword?

A Refers to the parent class

B Refers to the current object instance

C Refers to the class itself

D Refers to the method

Correct Answer: B. Refers to the current object instance

EXPLANATION

'this' is a reference to the current object instance. It's used to refer to instance variables, call other constructors, or pass object reference.

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Q.232 Easy OOP in Java

Which interface in Java represents a collection that does not allow duplicate elements?

A List

B Set

C Queue

D Map

Correct Answer: B. Set

EXPLANATION

Set interface ensures uniqueness and doesn't allow duplicate elements. HashSet, TreeSet are implementations of Set.

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Q.233 Easy OOP in Java

What is the purpose of the 'super' keyword in Java?

A To refer to the current object

B To refer to the parent class members

C To create a new object

D To call static methods

Correct Answer: B. To refer to the parent class members

EXPLANATION

The 'super' keyword is used to refer to the immediate parent class object. It's used to access parent class methods and constructors.

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Q.234 Easy OOP in Java

What will be the output?

class Parent {
void show() {
System.out.println("Parent");
}
}
class Child extends Parent {
void show() {
System.out.println("Child");
}
}
parent obj = new Child();
obj.show();

A Parent

B Child

C Compilation Error

D Runtime Error

Correct Answer: B. Child

EXPLANATION

This demonstrates method overriding and polymorphism. The actual object type is Child, so Child's show() method is called.

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Q.235 Easy OOP in Java

Which access modifier allows a member to be accessed only within the same package?

A public

B private

C protected

D default (package-private)

Correct Answer: D. default (package-private)

EXPLANATION

Default access (no modifier) allows access only within the same package. Protected allows same package and subclasses.

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Q.236 Easy OOP in Java

Which of the following is NOT a pillar of Object-Oriented Programming?

A Abstraction

B Polymorphism

C Compilation

D Encapsulation

Correct Answer: C. Compilation

EXPLANATION

The four pillars of OOP are Abstraction, Encapsulation, Inheritance, and Polymorphism. Compilation is a process, not a pillar of OOP.

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Q.237 Easy Basics & Syntax

Which of the following is a valid declaration of a two-dimensional array in Java that can store 3 rows and 4 columns of integers?

A int arr[][] = new int[3][4];

B int[] arr[] = new int[3][4];

C int[][] arr = new int[3][4];

D All of the above

Correct Answer: D. All of the above

EXPLANATION

All three declarations are syntactically valid in Java and represent the same 2D array structure. The position of brackets doesn't matter for 2D array declaration - they all create a 3x4 integer array.

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Q.238 Easy Basics & Syntax

Consider the following code. What will be printed?
String s = "Java";
s = s.concat(" Programming");
System.out.println(s.length());

A 4

B 8

C 17

D 19

Correct Answer: C. 17

EXPLANATION

"Java" has 4 characters. After concatenation with " Programming" (12 characters including space), the total length is 4 + 13 = 17 characters.

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Q.239 Easy Basics & Syntax

What will happen when you execute the following code?
int[] arr = new int[5];
System.out.println(arr[5]);

A Output: 0

B Output: null

C ArrayIndexOutOfBoundsException at runtime

D Compilation error

Correct Answer: C. ArrayIndexOutOfBoundsException at runtime

EXPLANATION

An array of size 5 has valid indices from 0 to 4. Accessing arr[5] throws ArrayIndexOutOfBoundsException at runtime because index 5 is out of bounds.

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Q.240 Easy Basics & Syntax

Which of the following statements about Java's garbage collection is TRUE?

A Garbage collection is guaranteed to run at specific time intervals

B The programmer must explicitly call System.gc() to free memory

C Garbage collection automatically reclaims memory used by unreferenced objects

D Java does not have automatic garbage collection mechanism

Correct Answer: C. Garbage collection automatically reclaims memory used by unreferenced objects

EXPLANATION

Java's garbage collector automatically identifies and reclaims memory of objects that are no longer referenced. While System.gc() can be suggested, it's not guaranteed to execute immediately.

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