What is the output of: System.out.println(true && false || true);

The correct answer is A: true. Evaluation: (true && false) || true = false || true = true. AND operator (&& has higher precedence than OR (||).

Which statement about multiple catch blocks is TRUE?

The correct answer is B: You can have multiple catch blocks, but only one will execute. Only one catch block executes for a thrown exception. The first matching catch block is executed.

Which of the following statements about 'this' keyword in Java is INCORRECT?

The correct answer is C: 'this' can be used in static methods. 'this' cannot be used in static methods because static methods are class-level and don't have an instance context. 'this' always refers to an instance.

Which of the following correctly implements the Factory Design Pattern principle in OOP?

The correct answer is B: Using a separate class with static methods to create and return objects of different types. The Factory Pattern uses a separate class (factory) with methods to create and return objects. This decouples object creation from usage.

Which lambda expression correctly implements a custom functional interface: public interface Math { int calculate(int a, int b); }

The correct answer is D: Both A and C. Both expressions are valid. Option A uses type inference while Option C explicitly specifies types. Both can implement the calculate method.

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Java Programming
Generics

Java OOP, collections, multithreading

49 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 21–30 of 49

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.21 Medium Generics

Consider the following code snippet:
public T processData(List

A T must be a subtype of the elements in the list

B The list can contain elements that are subtypes of T

C T and the wildcard bound are independent

D The list must contain exactly type T

Correct Answer: B. The list can contain elements that are subtypes of T

EXPLANATION

The wildcard '? extends T' means the list can contain any type that is a subtype of T. This allows reading from the list safely but restricts writing.

Test

Q.22 Medium Generics

How would you define a generic method that works with a pair of objects and returns the first one?

A T getFirst(T first, U second) { return first; }

B T getFirst(T first, T second) { return first; }

C public T getFirst(T first, U second) { return first; }

D Both A and C

Correct Answer: D. Both A and C

EXPLANATION

Both A and C define valid generic methods with multiple type parameters. C is more explicit with 'public' modifier, but both are functionally equivalent.

Test

Q.23 Medium Generics

What is the output?

List strings = new ArrayList();
List list = strings;
list.add(123);
String str = strings.get(0);
System.out.println(str);

A 123

B Compilation error

C Runtime ClassCastException

D null

Correct Answer: C. Runtime ClassCastException

EXPLANATION

Adding Integer 123 to raw type reference bypasses generics. When retrieving as String, a ClassCastException occurs at runtime.

Test

Q.24 Medium Generics

What happens when you use raw type List instead of List?

A Type safety is lost and unchecked warnings appear

B All elements are treated as Object

C Runtime ClassCastException may occur

D All of the above

Correct Answer: D. All of the above

EXPLANATION

Using raw types bypasses generic type checking, losing type safety. Elements are treated as Object at runtime, potentially causing ClassCastException when casting.

Test

Q.25 Medium Generics

Consider a generic interface: interface Comparable { int compareTo(T obj); }. How should a class implement this for String comparison?

A class MyClass implements Comparable { }

B class MyClass implements Comparable { }

C class MyClass implements Comparable { }

D Both B and C are valid

Correct Answer: D. Both B and C are valid

EXPLANATION

Option B directly specifies String, while Option C makes the class generic. Both are valid approaches to implement a generic interface.

Test

Q.26 Medium Generics

Which of the following will NOT compile?

A List numbers = new ArrayList();

B List

C List

D List objects = new ArrayList();

Correct Answer: D. List objects = new ArrayList();

EXPLANATION

Option D fails because List<Object> cannot reference ArrayList<String>. Generics are invariant. Options A, B, C are valid (covariance with extends, contravariance with super).

Test

Q.27 Medium Generics

What does List represent in Java generics?

A List of unknown type

B List of any type

C List that can hold any single unknown type

D All of the above

Correct Answer: D. All of the above

EXPLANATION

List<?> is an unbounded wildcard that represents a list of unknown type. You can read from it (get Object), but cannot write to it (except null). Both A, B, and C are correct interpretations.

Test

Q.28 Medium Generics

Consider: public static T findMax(T a, T b) { return a; }. What is the issue with calling findMax(5, 3.5)?

A T cannot be inferred because int and double are different

B The method will compile and run without issues

C T will be Object type

D Runtime exception will occur

Correct Answer: A. T cannot be inferred because int and double are different

EXPLANATION

The type parameter T cannot simultaneously be int and double. The compiler cannot infer a single type T that satisfies both arguments, resulting in a compilation error.

Test

Q.29 Medium Generics

Which statement correctly defines a generic class with multiple type parameters and bounds?

A class Container { }

B class Container extends Number { }

C class Container { }

D class Container extends { }

Correct Answer: C. class Container { }

EXPLANATION

Multiple type parameters with bounds must be comma-separated and each can have its own upper bound. Option C shows correct syntax with recursive bound on T and bound on K.

Test

Q.30 Medium Generics

Consider the declaration: List

A List of Integer and its subclasses

B List of Integer and its superclasses

C List of any type

D List of Number and Integer only

Correct Answer: B. List of Integer and its superclasses

EXPLANATION

'? super Integer' is a lower bounded wildcard that accepts Integer and all its superclasses like Number, Object. This allows write operations with Integer values.

Test

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