What is the output of: System.out.println(5 % 2 + 3 * 2 - 1);?

The correct answer is A: 6. Following operator precedence: 5%2=1, 3*2=6, then 1+6-1=6

Which scenario can lead to livelock in multithreading?

The correct answer is A: Two threads continuously change state in response to each other but never make progress. Livelock occurs when threads are not blocked but continuously change state in response to each other (like two people trying to pass each other), preventing progress. This differs from deadlock where threads are blocked.

What exception is thrown when you try to add a null value to a TreeSet?

The correct answer is A: NullPointerException. TreeSet uses comparator or natural ordering, which cannot handle null values, throwing NullPointerException during insertion.

What happens when you try to read from a closed stream in Java?

The correct answer is B: Throws IOException. Attempting to read from a closed stream throws an IOException. The stream must be open for read operations.

In a producer-consumer scenario using BlockingQueue, what happens when a consumer thread calls take() on an empty queue?

The correct answer is B: It blocks until a producer adds an element. BlockingQueue's take() method blocks the calling thread until an element becomes available. This is safer and more efficient than busy-waiting. NoSuchElementException is thrown by non-blocking operations like remove().

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Java Programming

Java OOP, collections, multithreading

212 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 31–40 of 212

Topics in Java Programming

All Basics & Syntax 100 OOP in Java 100 Collections Framework 100 Multithreading 100 Exception Handling 100 I/O Streams 100 JDBC 100 Generics 100 Lambda Expressions 100 Spring Framework Basics 58

Q.31 Hard Generics

Which Java feature was introduced specifically to support generics compilation?

A Bridge methods

B Reflection API

C Annotations

D Lambda expressions

Correct Answer: A. Bridge methods

EXPLANATION

Bridge methods are synthetic methods generated during compilation to maintain polymorphism with generic types and type erasure.

Test

Q.32 Hard Generics

What output will this produce?
java
List

A Compiles and runs successfully, prints 5

B Compilation error

C Runtime ClassCastException

D Returns null

Correct Answer: C. Runtime ClassCastException

EXPLANATION

With lower-bounded wildcard (? super Integer), you can add Integer but retrieval returns Object. Casting Object to Integer without proper type causes ClassCastException.

Test

Q.33 Hard Generics

Which statement about generic array creation is correct?

A new ArrayList[10] is valid

B new List[10] is valid but produces warning

C Generic arrays cannot be created directly; use new ArrayList() instead

D Generic arrays are valid in Java 8+

Correct Answer: C. Generic arrays cannot be created directly; use new ArrayList() instead

EXPLANATION

You cannot create arrays of generic types due to type erasure and heap pollution risks. Use Collection framework instead of arrays.

Test

Q.34 Hard Generics

What is the compiled bytecode signature of this generic method?
public T findMin(T[] arr)

A public Comparable findMin(Comparable[] arr)

B public Object findMin(Object[] arr)

C public Comparable findMin(Comparable[] arr)

D public Comparable findMin(Comparable[] arr) with bridge method

Correct Answer: A. public Comparable findMin(Comparable[] arr)

EXPLANATION

Type erasure replaces T with its bound Comparable. The method signature becomes public Comparable findMin(Comparable[] arr).

Test

Q.35 Hard Generics

What is the difference between List and List in practical usage?

A They are identical

B List can accept any type; List cannot accept anything

C List can add Objects; List can only add null

D List is deprecated in favor of List

Correct Answer: C. List can add Objects; List can only add null

EXPLANATION

List<Object> accepts Object and its subclasses for adding. List<?> (unbounded wildcard) is more flexible for reading but restrictive for writing (only null).

Test

Q.36 Hard Generics

Consider this declaration: public static List createList(). Which statement about type inference is correct?

A Compiler always knows the type T

B Type T is inferred from context where method is called

C Type T must always be explicitly specified

D Compiler defaults T to Object

Correct Answer: B. Type T is inferred from context where method is called

EXPLANATION

Java's type inference deduces T from the assignment context. E.g., 'List<String> list = createList()' infers T as String.

Test

Q.37 Hard Generics

What will happen when you compile and run this code?
java
List strings = Arrays.asList("a", "b", "c");
List raw = strings;
raw.add(123);
String s = strings.get(3);

A Compiles successfully and runs without error

B Compilation error due to raw type usage

C Compiles with warning, throws ClassCastException at runtime

D Compiles and throws ArrayIndexOutOfBoundsException

Correct Answer: C. Compiles with warning, throws ClassCastException at runtime

EXPLANATION

Assigning generic type to raw type suppresses type checking. The Integer added bypasses the type system, causing ClassCastException when retrieved as String.

Test

Q.38 Hard Generics

How would you correctly use generics in a recursive type bound scenario?

A class Node { Node next; }

B class Node { Node next; }

C class Node extends T { }

D class Node { }

Correct Answer: A. class Node { Node next; }

EXPLANATION

Option A demonstrates recursive type bound (also called F-bounded polymorphism), which allows a type to reference itself in its bound. This is commonly used in builder patterns and comparators.

Test

Q.39 Hard Generics

Which of the following represents valid bounded wildcard usage for a method that processes collections?

A public void process(Collection

B public void process(Collection

C public void process(Collection col) { col.add(5); }

D public void process(Collection col) { col.add(5); }

Correct Answer: B. public void process(Collection

EXPLANATION

Only option B allows adding elements safely. '? super Integer' means the collection can hold Integer or any supertype. Option A prevents adding, Option C prevents adding, Option D restricts to exactly Number.

Test

Q.40 Hard Generics

What is the compiled signature of this generic method?
public void sort(T[] array)

A public void sort(Number[] array)

B public void sort(Comparable[] array)

C public void sort(Object[] array)

D Type erasure uses the first bound: public void sort(Number[] array)

Correct Answer: D. Type erasure uses the first bound: public void sort(Number[] array)

EXPLANATION

With multiple bounds using '&', type erasure replaces T with the first bound. Here, Number is the first bound, so T is replaced with Number.

Test

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