Question 1

Which keyword is used to prevent a class from being inherited in Java?

Accepted Answer

final. The 'final' keyword prevents a class from being subclassed. A final method cannot be overridden.

Question 2

What is the output of: String s = "Hello"; s.concat(" World"); System.out.println(s);

Accepted Answer

Hello. Strings in Java are immutable. concat() returns a new String but doesn't modify s. To see 'Hello World', you'd need s = s.concat(' World').

Question 3

Which collection class allows duplicate elements and maintains insertion order?

Accepted Answer

ArrayList. ArrayList allows duplicates and maintains insertion order. HashSet and TreeSet do not allow duplicates. HashMap stores key-value pairs.

Question 4

What does JVM stand for?

Accepted Answer

Java Virtual Machine. JVM (Java Virtual Machine) is an abstract machine that executes Java bytecode. It provides platform independence.

Question 5

What is autoboxing in Java?

Accepted Answer

Automatic conversion between primitive types and their wrapper classes. Autoboxing is the automatic conversion of a primitive type (e.g., int) to its wrapper class (Integer). Unboxing is the reverse.

Java MCQ Quiz

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