What happens when Thread.interrupt() is called on a thread?

The correct answer is A: Sets the interrupt flag; the thread can check it using isInterrupted(). interrupt() sets an internal interrupt flag. The thread must check this flag using isInterrupted() or interrupted() and handle it appropriately.

What is the primary purpose of Generics in Java?

The correct answer is A: To provide type safety and eliminate type casting. Generics enable type safety at compile time and eliminate the need for explicit type casting, reducing runtime errors.

What is the output of Collections.frequency(list, null) if list contains null elements?

The correct answer is A: Returns count of null elements. Collections.frequency() correctly handles null values and returns the count of null elements in the collection.

You need to read a file line by line efficiently. Which approach is best?

The correct answer is B: BufferedReader with readLine(). BufferedReader with readLine() is the most efficient and convenient way to read files line by line. It provides buffering and a dedicated method for reading lines.

How would you implement batch processing in JDBC for multiple INSERT operations?

The correct answer is A: Use addBatch() and executeBatch() methods. addBatch() adds SQL command to batch, executeBatch() executes all batched commands at once, improving performance significantly for multiple operations.

Home

Home › Subjects › Java Programming › Generics

Java Programming
Generics

Java OOP, collections, multithreading

26 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 11–20 of 26

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.11 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

Q.12 Hard Generics

Which generic wildcard usage follows the consumer pattern correctly?

A public void consume(List

B public void consume(List

C public void consume(List list) { list.add(new Integer(5)); }

D public void consume(List list) { list.add(new Integer(5)); }

Correct Answer: B. public void consume(List

EXPLANATION

Consumer pattern uses '? super T' (lower bound). This allows adding elements safely. Option A (producer pattern) only allows reading, and Options C and D restrict type flexibility.

Test

Q.13 Hard Generics

Which statement correctly implements a generic factory method?

A public static T create(Class clazz) { return new T(); }

B public static T create(Class clazz) throws Exception { return clazz.newInstance(); }

C public static T create(T t) { return (T) new Object(); }

D public T create() { return new T(); }

Correct Answer: B. public static T create(Class clazz) throws Exception { return clazz.newInstance(); }

EXPLANATION

Cannot instantiate generic type T directly. Using Class<T>.newInstance() is a valid pattern (though deprecated in newer Java versions in favor of getConstructor()). Option A is invalid.

Test

Q.14 Hard Generics

Which statement about generic constructors is TRUE?

A Generic constructors must be in generic classes only

B Non-generic classes can have generic constructors

C Constructor type parameters are independent of class type parameters

D Both B and C

Correct Answer: D. Both B and C

EXPLANATION

Generic constructors can exist in non-generic classes. Constructor's type parameters are separate from and independent of the class's type parameters.

Test

Q.15 Hard Generics

What is the PECS principle in generics?

A Producer Extends, Consumer Super

B Public Extends, Consumer Sets

C Parameter Encapsulation and Class Structure

D Polymorphic Extension and Class Signatures

Correct Answer: A. Producer Extends, Consumer Super

EXPLANATION

PECS (Producer Extends, Consumer Super) is a mnemonic for wildcard bounds: use '? extends' when reading (producing), use '? super' when writing (consuming).

Test

Q.16 Hard Generics

Can you create an instance of generic type parameter directly like: T obj = new T();?

A Yes, always possible

B No, because type information is erased at runtime

C Yes, only if T extends Serializable

D Only with reflection

Correct Answer: B. No, because type information is erased at runtime

EXPLANATION

Due to type erasure, T is replaced with Object at runtime, and you cannot instantiate Object with new T(). You need reflection or pass Class<T> as parameter.

Test

Q.17 Hard Generics

What is the difference between and ?

A No difference; both are equivalent

B First ensures T is comparable with itself; second is a raw type

C First is deprecated in Java 8+

D Second provides better type safety

Correct Answer: B. First ensures T is comparable with itself; second is a raw type

EXPLANATION

<T extends Comparable<T>> is a recursive bound ensuring T implements Comparable of its own type. <T extends Comparable> uses raw type, losing type information.

Test

Q.18 Hard Generics

Which generic declaration allows a method to accept List of any type?

A public void process(List rawList) { }

B public void process(List list) { }

C public void process(List list) { }

D All of the above

Correct Answer: D. All of the above

EXPLANATION

All three approaches allow processing lists of any type, though they differ: raw type (unsafe), unbounded wildcard (read-only), and type parameter (flexible).

Test

Q.19 Hard Generics

What is the key difference between '? extends T' and '? super T' in practical usage?

A Extends is for reading data safely, Super is for writing data safely

B Extends is for writing, Super is for reading

C They have no practical difference

D Extends is for classes, Super is for interfaces

Correct Answer: A. Extends is for reading data safely, Super is for writing data safely

EXPLANATION

Upper bounds (? extends T) are safe for reading because the compiler knows it's at least T. Lower bounds (? super T) are safe for writing because you can pass T or any superclass.

Test

Q.20 Hard Generics

Consider: Map

A A List of unknown element type

B A List

C Any List type

D Nothing can be safely retrieved

Correct Answer: A. A List of unknown element type

EXPLANATION

The value type is '? extends List<?>', so you get a List with unknown element type. The exact subtype is unknown at compile-time.

Test

1 2 3

All Subjects & Topics

Govt. Exams

Entrance Exams

Teacher Exams

Subjects

Quick Links

Java Programming Generics

Java Programming
Generics