What is the difference between commit() and rollback() in JDBC transactions?

The correct answer is A: commit() saves changes, rollback() undoes them. commit() permanently saves all changes made during the transaction, while rollback() discards all changes and reverts to the previous state.

In a lambda expression, what does the arrow (->) operator represent?

The correct answer is B: Separation between parameters and body. The arrow (->) in lambda expressions separates the parameter list on the left from the method body on the right. It's a syntax element specific to lambda expressions.

What is the primary advantage of using PreparedStatement over Statement?

The correct answer is A: Faster execution and SQL injection prevention. PreparedStatement offers faster execution due to precompilation and prevents SQL injection through parameterized queries using placeholders (?).

Which of the following will NOT compile?

The correct answer is D: List objects = new ArrayList();. Option D fails because List cannot reference ArrayList. Generics are invariant. Options A, B, C are valid (covariance with extends, contravariance with super).

Which of the following lambda expressions will compile successfully?

The correct answer is D: A and C. Both A and C are valid. Option B fails because variable x is already declared as parameter. Option C uses var keyword (Java 10+).

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Java Programming

Java OOP, collections, multithreading

476 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 81–90 of 476

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.81 Medium Lambda Expressions

What is the type of the following lambda expression: x -> x.length()?

A Function

B Consumer

C Supplier

D Predicate

Correct Answer: A. Function

EXPLANATION

Function<T,R> takes one argument of type T and returns R. Here String -> Integer (length), so Function<String, Integer>.

Test

Q.82 Medium Lambda Expressions

Which of the following lambda expressions is invalid?

A () -> System.out.println("Hello")

B x -> x * 2

C (int x, int y) -> { return x + y; }

D -> x + y

Correct Answer: D. -> x + y

EXPLANATION

Lambda must have parameter list (even if empty with ()). Missing parameter list '() -> x + y' is invalid syntax.

Test

Q.83 Medium Generics

In a microservices architecture, you're designing a Response wrapper class that should work with any data type, including primitives when boxed. Which implementation is correct?

A public class Response { private T data; private int statusCode; }

B public class Response { private Object data; private int statusCode; }

C public class Response { private T data; private int statusCode; }

D public class Response { private T data; private S statusCode; }

Correct Answer: A. public class Response { private T data; private int statusCode; }

EXPLANATION

Option A provides proper generic type safety without unnecessary constraints. While Option C adds a Serializable bound (sometimes desirable), Option A is the most flexible and commonly used pattern for generic response wrappers.

Test

Q.84 Medium Generics

A utility class needs a method that accepts a List containing elements that are instances of a specific class or its subclasses. Which wildcard notation should be used?

A public static void process(List

B public static void process(List list)

C public static void process(List

D public static void process(List list)

Correct Answer: A. public static void process(List

EXPLANATION

'? extends TargetClass' creates a covariant wildcard allowing lists of TargetClass or any subclass. This is ideal for reading operations when you need polymorphic list handling.

Test

Q.85 Medium Generics

A developer creates a generic method that accepts a collection of numbers and calculates their sum. Which type parameter declaration would be most appropriate for this scenario?

A public static double calculateSum(List numbers)

B public static double calculateSum(List numbers)

C public static double calculateSum(List numbers)

D public static double calculateSum(List numbers)

Correct Answer: A. public static double calculateSum(List numbers)

EXPLANATION

Using 'T extends Number' establishes an upper bound, allowing the method to work with any Number subclass (Integer, Double, Float, etc.) while providing type safety and access to Number methods.

Test

Q.86 Medium Generics

What is the runtime class object for this generic variable?
java
List list = new ArrayList();
Class c = list.getClass();

A java.util.List

B java.util.ArrayList

C java.util.ArrayList

D java.lang.Object

Correct Answer: C. java.util.ArrayList

EXPLANATION

Due to type erasure, getClass() returns ArrayList without generic parameters. Generic information exists only at compile time.

Test

Q.87 Medium Generics

Which of these is a valid generic interface implementation?

A class MyClass implements Comparable

B class MyClass implements Comparable

C class MyClass extends Comparable

D class MyClass implements Comparable

Correct Answer: A. class MyClass implements Comparable

EXPLANATION

Implementing generic interfaces requires specifying the type parameter. 'implements Comparable<MyClass>' is the proper way to implement.

Test

Q.88 Medium Generics

What is the PECS principle in Java Generics?

A Public Extends Collections Structure

B Producer Extends, Consumer Super

C Parameter Extends Comparable Supports

D Polymorphic Extends Class Super

Correct Answer: B. Producer Extends, Consumer Super

EXPLANATION

PECS (Producer Extends, Consumer Super) is a guideline: use 'extends' for producers (reading) and 'super' for consumers (writing).

Test

Q.89 Medium Generics

What does 'covariance' mean in the context of Java Generics?

A Types vary together in the same direction

B Types vary in opposite directions

C Types do not vary at all

D Types are interchangeable

Correct Answer: A. Types vary together in the same direction

EXPLANATION

Covariance means if Dog is a subtype of Animal, then Producer<Dog> is a subtype of Producer<Animal>. Achieved using upper-bounded wildcards.

Test

Q.90 Medium Generics

Which wildcard usage follows the Producer pattern?

A List

B List

C List

D List

Correct Answer: B. List

EXPLANATION

Producer (Get-Only pattern) uses upper-bounded wildcard (? extends T). It's used when you want to read/produce elements of specific types.

Test

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