Java Programming Questions & Answers

Q.891 Medium Basics & Syntax

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

A To refer to the parent class

B To refer to the current object instance

C To create a new object

D To access static variables

Correct Answer: B. To refer to the current object instance

EXPLANATION

'this' is a reference variable that refers to the current object instance. It is used to distinguish instance variables from local variables with the same name, or to pass the current object as a parameter.

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Q.892 Easy Basics & Syntax

What will be the result of: int a = 10; int b = 20; System.out.println(a + b + "Java");?

A "30Java"

B "1020Java"

C "Java30"

D Compilation error

Correct Answer: A. "30Java"

EXPLANATION

When + operator is used with numeric values first, they are added (10 + 20 = 30), and then concatenated with the string "Java", resulting in "30Java".

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Q.893 Easy Basics & Syntax

Which keyword is used to create a constant variable in Java that cannot be modified after initialization?

A static

B const

C final

D immutable

Correct Answer: C. final

EXPLANATION

The 'final' keyword is used to declare constants in Java. Once a final variable is assigned a value, it cannot be changed. 'const' is a reserved keyword but not used in Java.

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Q.894 Hard Basics & Syntax

What is the output of: int x = 5; System.out.println(x++ + ++x);

A 12

B 11

C 10

D 13

Correct Answer: B. 11

EXPLANATION

x++ uses current value (5) then increments, ++x increments first then uses value (7). Order of evaluation: 5 + 7 = 12. However, x becomes 7 after ++x.

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Q.895 Hard Basics & Syntax

Consider: class Parent { Parent() { System.out.println("P"); } } class Child extends Parent { Child() { System.out.println("C"); } } public static void main(String[] args) { new Child(); }

A C

B P

C P C

D C P

Correct Answer: C. P C

EXPLANATION

Child constructor implicitly calls super() first, executing Parent constructor. Output: Parent prints 'P', then Child prints 'C'.

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Q.896 Hard Basics & Syntax

Which of the following will throw a NullPointerException? String s = null; System.out.println(s.length());

A s = null

B System.out

C s.length()

D println()

Correct Answer: C. s.length()

EXPLANATION

Calling a method on a null reference throws NullPointerException. s.length() tries to invoke method on null, causing the exception.

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Q.897 Hard Basics & Syntax

What will be the output? class Test { public static void main(String[] args) { int x = 10; { int x = 20; System.out.println(x); } System.out.println(x); } }

A 10 20

B 20 10

C 20 20

D Compilation Error

Correct Answer: B. 20 10

EXPLANATION

A block scope creates a new variable x = 20 which shadows the outer x. First print outputs 20, then the block ends, outer x (10) is printed.

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Q.898 Medium Basics & Syntax

Which of the following is a feature of Java 8 that allows functional programming?

A Lambda expressions

B Generics

C Annotations

D Enums

Correct Answer: A. Lambda expressions

EXPLANATION

Lambda expressions were introduced in Java 8, enabling functional programming. Syntax: (parameters) -> expression or statement

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Q.899 Medium Basics & Syntax

Consider: String s1 = "Java"; String s2 = new String("Java"); System.out.println(s1 == s2);

A true

B false

C Compilation Error

D Runtime Error

Correct Answer: B. false

EXPLANATION

s1 is created in string pool, s2 is a new object in heap. Though content is same, references are different, so == returns false.

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Q.900 Medium Basics & Syntax

What is the difference between == and equals() in Java?

A Both are identical

B == compares values, equals() compares references

C == compares references, equals() compares values

D equals() is only for objects, == is for primitives

Correct Answer: C. == compares references, equals() compares values

EXPLANATION

== compares object references (memory addresses). equals() method compares actual content/values and can be overridden.

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