Consider this code: public T getMax(T a, T b) { return a.compareTo(b) > 0 ? a : b; } What is the benefit of this recursive bound ?

The correct answer is A: Ensures type safety by guaranteeing T implements Comparable with itself. Recursive bound ensures that T implements Comparable interface specifically for comparing with its own type, providing type safety.

Which of the following is thread-safe?

The correct answer is C: ConcurrentHashMap. ConcurrentHashMap is thread-safe and uses bucket-level locking. HashMap, TreeMap, and LinkedHashMap are not thread-safe.

What is the difference between notify() and notifyAll()?

The correct answer is A: notify() wakes one waiting thread, notifyAll() wakes all waiting threads. notify() wakes up a single thread that is waiting on the object's monitor, while notifyAll() wakes up all threads waiting on that object.

How does Java 8+ handle hash collisions in HashMap differently?

The correct answer is B: Converts bucket linked list to Red-Black tree when size exceeds threshold. Java 8+ introduced tree nodes: when a bucket's linked list size exceeds TREEIFY_THRESHOLD (8), it converts to a Red-Black tree for better performance (O(log n) vs O(n)).

Which of the following will result in a compilation error? class Test { public void method1() { } public void method1(int x) { } }

The correct answer is C: No error, valid code. This is valid method overloading. Two methods with same name but different parameters (method signature) is allowed in Java.

Home

Home › Subjects › Java Programming › Basics & Syntax

Java Programming
Basics & Syntax

Java OOP, collections, multithreading

50 Q 10 Topics Take Mock Test

Difficulty: All Easy Medium Hard 1–10 of 50

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.1 Medium Basics & Syntax

In Java, what is the relationship between an interface and a class in terms of implementation?

A A class can implement multiple interfaces but can extend only one class

B A class can extend multiple interfaces and implement one class

C A class can only implement one interface and extend one class

D An interface and a class cannot be used together in Java

Correct Answer: A. A class can implement multiple interfaces but can extend only one class

EXPLANATION

Java supports multiple interface implementation but single class inheritance. A class uses 'implements' keyword for interfaces and 'extends' for classes. This is a fundamental OOP concept.

Test

Q.2 Medium Basics & Syntax

Which of the following statements about Java's String class is TRUE?

A Strings are mutable objects in Java

B The String class is marked as 'final' to prevent modification of its behavior

C Creating a new String using 'new' keyword always creates a new object in the string pool

D String concatenation using '+' operator is more efficient than StringBuilder for single operations

Correct Answer: B. The String class is marked as 'final' to prevent modification of its behavior

EXPLANATION

The String class is declared as 'final' in Java, which prevents inheritance and ensures immutability. Strings are immutable, 'new' creates objects in heap not pool, and StringBuilder is generally better for concatenation.

Test

Q.3 Medium Basics & Syntax

Consider a real-world scenario where you need to implement a logging system. Which access modifier would you use for internal helper methods that should not be accessible outside the class?

A public

B protected

C private

D default (package-private)

Correct Answer: C. private

EXPLANATION

'private' access modifier restricts the method to be accessible only within the same class, making it ideal for internal helper methods. This follows encapsulation principles.

Test

Q.4 Medium Basics & Syntax

Which of the following correctly demonstrates method overloading in Java?

A public void display(int x) { } public int display(int y) { return 0; }

B public void display(int x) { } public void display(float x) { }

C public void display(int x) { } private void display(int x) { }

D public void display(int x) { } public void Display(int x) { }

Correct Answer: B. public void display(int x) { } public void display(float x) { }

EXPLANATION

Method overloading requires methods with the same name but different parameter types or number of parameters. Option A has different return types (not sufficient), C has different access modifiers (not overloading), D has different case names (different methods).

Test

Q.5 Medium Basics & Syntax

Consider a scenario where you need to create a variable that can hold references to objects of any type. Which of the following approaches would be most appropriate in Java 2024 standards?

A Use raw type: List myList = new ArrayList();

B Use generics: List myList = new ArrayList();

C Use Object type: Object obj = new Object();

D Use var keyword: var myList = new ArrayList();

Correct Answer: B. Use generics: List myList = new ArrayList();

EXPLANATION

Using generics with wildcards (List<?>) is the safest and most type-safe approach to handle objects of any type in modern Java. The 'var' keyword is also acceptable but wildcards provide better type checking.

Test

Q.6 Medium Basics & Syntax

What will be the output of the following code?
String str1 = "Hello";
String str2 = new String("Hello");
System.out.println(str1 == str2);

A true

B false

C null

D Compilation error

Correct Answer: B. false

EXPLANATION

The '==' operator compares object references, not content. str1 refers to the string pool while str2 is a new object in heap memory, hence they have different references.

Test

Q.7 Medium Basics & Syntax

Which method is called automatically when an object is garbage collected?

A finalize()

B destroy()

C delete()

D cleanup()

Correct Answer: A. finalize()

EXPLANATION

The finalize() method is called by the garbage collector before an object is destroyed. It can be used to perform cleanup operations, though it's generally not recommended in modern Java.

Test

Q.8 Medium Basics & Syntax

Which of the following will compile and run without errors?

A public static void main() { }

B public static void main(String[] args) { }

C public void main(String[] args) { }

D static void main(String[] args) { }

Correct Answer: B. public static void main(String[] args) { }

EXPLANATION

The correct signature for the main method is 'public static void main(String[] args)'. It must be public, static, void, named 'main', and accept a String array parameter. Any deviation will not be recognized as the entry point.

Test

Q.9 Medium Basics & Syntax

Which of the following correctly represents variable declaration and initialization in Java?

A int x; x = 5.5;

B double y = 10;

C boolean flag = true;

D String name = 123;

Correct Answer: C. boolean flag = true;

EXPLANATION

Option C is correct. Option A causes a compilation error (cannot assign double to int). Option B works but there's implicit conversion. Option D causes a compilation error (cannot assign int to String).

Test

Q.10 Medium Basics & Syntax

Which statement about constructors is INCORRECT?

A Constructors can be overloaded

B Constructors must return a value

C Constructors are called automatically when an object is created

D A class can have multiple constructors

Correct Answer: B. Constructors must return a value

EXPLANATION

Constructors do NOT have a return type, not even void. They automatically initialize objects when created. They can be overloaded and a class can have multiple constructors with different parameters.

Test

1 2 3…5

All Subjects & Topics

Govt. Exams

Entrance Exams

Teacher Exams

Subjects

Quick Links

Java Programming Basics & Syntax

Java Programming
Basics & Syntax