Java Quiz - Multiple Choice Questions

Welcome to our Java Quiz! Whether you’re a beginner looking to test your Java knowledge or a seasoned developer aiming to refresh your skills, this quiz is for you. Java, known for its portability across platforms and robustness, remains one of the most popular programming languages. In this blog post, we’ve compiled a set of 40 simple multiple-choice questions covering fundamental Java concepts. Each question is accompanied by an answer and a concise explanation to enhance your understanding. So, let’s dive in and challenge your Java expertise!

1. Which of these data types is used to store a single character in Java?

a) char

b) String

c) int

d) byte

Answer:

a) char

Explanation:

In Java, the 'char' data type is used to store a single character.

2. What is the size of the float and double in Java?

a) 32 and 64

b) 64 and 32

c) 16 and 32

d) 32 and 32

Answer:

a) 32 and 64

Explanation:

In Java, float is a 32-bit IEEE 754 floating-point and double is a 64-bit IEEE 754 floating-point.

3. Which of these is used for making an object immutable in Java?

a) final

b) static

c) abstract

d) synchronized

Answer:

a) final

Explanation:

The 'final' keyword makes a variable value unchangeable (immutable) in Java.

4. What does the expression float a = 35 / 0 return?

a) 0

b) Not a Number

c) Infinity

d) An exception is thrown

Answer:

c) Infinity

Explanation:

In Java, dividing a float by zero does not throw an ArithmeticException but results in Infinity.

5. In Java, which of these keywords is used to inherit a class?

a) super

b) this

c) extend

d) extends

Answer:

d) extends

Explanation:

In Java, 'extends' is the keyword used for inheriting the properties of a class.

6. What is the default value of a static variable?

a) null

b) 0

c) Depends on the type

d) Not assigned

Answer:

c) Depends on the type

Explanation:

In Java, static variables get default values. For numbers, it's 0; for booleans, it's false; and for object references, it's null.

7. Which method can't be overridden in Java?

a) Static method

b) Instance method

c) Final method

d) Abstract method

Answer:

c) Final method

Explanation:

Methods declared as final cannot be overridden in Java.

8. What does the 'instanceof' keyword check?

a) If an object is an instance of a specific class

b) The existence of an instance in the memory

c) Compatibility between two variables

d) If a class inherits another class

Answer:

a) If an object is an instance of a specific class

Explanation:

The 'instanceof' keyword checks whether an object is an instance of a specified class or interface.

9. In Java, which of these access specifiers has the most restrictive access?

a) private

b) protected

c) public

d) default

Answer:

a) private

Explanation:

The 'private' access specifier is the most restrictive, limiting access to the defining class only.

10. What is the purpose of the 'super' keyword in Java?

a) To call methods of the parent class

b) To refer to the immediate parent class instance variable

c) Both a) and b)

d) To make a method more efficient

Answer:

c) Both a) and b)

Explanation:

The 'super' keyword is used to refer to immediate parent class variables and methods.

11. Which collection class in Java allows you to grow or shrink its size and provides indexed access to its elements, but is not synchronized?

a) HashSet

b) LinkedHashMap

c) ArrayList

d) HashTable

Answer:

c) ArrayList

Explanation:

ArrayList in Java can dynamically grow or shrink in size and provides indexed access to its elements but is not synchronized, meaning it's not thread-safe by default.

12. Which of these is a valid way to obtain a new String "Hello World"?

a) String s = "Hello " + "World";

b) new String("Hello World");

c) Both a) and b)

d) String s = "Hello", s += " World";

Answer:

c) Both a) and b)

Explanation:

Both concatenation using '+' and the new String constructor are valid ways to create a new String in Java.

13. What is the base class for all classes in Java?

a) Main

b) Object

c) Class

d) Parent

Answer:

b) Object

Explanation:

In Java, 'Object' is the base class for all the classes. Every class is a descendant, direct or indirect, of the Object class.

14. What does the hashCode() method of an object return?

a) A unique ID of the object

b) Memory reference of the object

c) A hash value representing the object

d) Length of the object

Answer:

c) A hash value representing the object

Explanation:

The hashCode() method returns a hash value that represents the instance of the object.

15. In Java, which of these keywords is used to define a package?

a) package

b) Package

c) pkg

d) Pkg

Answer:

a) package

Explanation:

In Java, the 'package' keyword is used to define a package that includes the classes.

16. Which of these is a valid entry point for a Java application?

a) public static void start(String[] args)

b) public void main(String[] args)

c) public static void main(String[] args)

d) public static int main(String[] args)

Answer:

c) public static void main(String[] args)

Explanation:

The entry point for a Java application is the main method with the signature public static void main(String[] args).

17. In Java, which keyword is used to inherit properties of a class?

a) super

b) this

c) extends

d) implements

Answer:

c) extends

Explanation:

The 'extends' keyword is used in Java for a class to inherit the properties of another class.

18. What is the result of compiling and running a Java program with the filename 'Main.java' containing multiple classes?

a) Error, as only one class is allowed per file

b) All classes are compiled into a single Main.class file

c) Each class is compiled into its own .class file

d) Only the Main class is compiled

Answer:

c) Each class is compiled into its own .class file

Explanation:

In Java, each class in a file is compiled into its own separate .class file, regardless of the file name.

19. What does the 'static' keyword in Java signify?

a) The method or variable belongs to the instance of a class

b) The method or variable belongs to the class and can be accessed directly

c) The method or variable is constant and cannot be changed

d) The method or variable is synchronized across threads

Answer:

b) The method or variable belongs to the class and can be accessed directly

Explanation:

The 'static' keyword in Java indicates that the method or variable is not tied to a specific instance but belongs to the class itself.

20. How does Java achieve platform independence?

a) Through the use of the Java Virtual Machine (JVM)

b) By compiling into native machine code

c) Through the use of web technologies

d) By interpreting the code at runtime

Answer:

a) Through the use of the Java Virtual Machine (JVM)

Explanation:

Java achieves platform independence through the use of the Java Virtual Machine (JVM), which allows Java programs to run on any platform that has a JVM implementation.

21. Which of these is not a valid Java type?

a) byte

b) short

c) string

d) long

Answer:

c) string

Explanation:

In Java, 'string' is not a valid type. The correct type for a sequence of characters is 'String' with an uppercase 'S'.

22. How are Java objects stored in memory?

a) In Stack

b) In Heap

c) In Queue

d) In Tree

Answer:

b) In Heap

Explanation:

In Java, objects are stored in the heap memory. The heap is used for dynamic memory allocation for Java objects and JRE classes at runtime.

23. What is the default value of a boolean in Java?

a) true

b) false

c) null

d) 0

Answer:

b) false

Explanation:

In Java, the default value of a boolean primitive type is false.

24. In Java, what is the term for the process of defining two or more methods within the same class that have the same name but different parameters?

a) Method overloading

b) Method overriding

c) Method duplication

d) Method calling

Answer:

a) Method overloading

Explanation:

Method overloading in Java is the ability to create multiple methods of the same name with different implementations and parameters.

25. Which of these is a valid declaration of a char in Java?

a) char ch = 'xaa';

b) char ch = 'x5';

c) char ch = '\u0057';

d) char ch = '\ua432';

Answer:

c) char ch = '\u0057'

Explanation:

In Java, a char can be declared using Unicode representations like '\u0057'. The other options are either invalid or not following the correct syntax for character declaration.

26. Which interface does java.util.Hashtable implement?

a) Map

b) List

c) Set

d) HashTable

Answer:

a) Map

Explanation:

java.util.Hashtable implements the Map interface, which represents a key-value store.

27. In Java, what is the purpose of the 'finally' block in exception handling?

a) To handle the exception

b) To execute code after a try/catch block, regardless of whether an exception was thrown

c) To declare exceptions

d) To run code only if an exception is caught

Answer:

b) To execute code after a try/catch block, regardless of whether an exception was thrown

Explanation:

The 'finally' block in Java is used to execute code after the try/catch blocks have been executed, regardless of whether an exception was thrown or not.

28. Which keyword in Java is used to create a subclass?

a) super

b) this

c) subclass

d) extends

Answer:

d) extends

Explanation:

The 'extends' keyword is used in Java to create a subclass that inherits the properties and behavior from a superclass.

29. How do you access a static variable in Java?

a) Through an object of the class

b) Directly by the class name

c) Through a method only

d) Static variables are not accessible

Answer:

b) Directly by the class name

Explanation:

Static variables in Java are accessed directly by the class name and don't require an object instance for access.

30. What is the return type of a method that does not return any value?

a) null

b) void

c) 0

d) empty

Answer:

b) void

Explanation:

In Java, if a method does not return a value, its return type is specified as 'void'.

31. Which Java feature is used for managing memory automatically?

a) Inheritance

b) Encapsulation

c) Garbage Collection

d) Abstraction

Answer:

c) Garbage Collection

Explanation:

Garbage Collection in Java is a process that automatically identifies and frees up memory that is no longer in use, thus managing memory automatically.

32. What does the 'synchronized' keyword in Java do?

a) Prevents code execution in multiple threads simultaneously

b) Synchronizes method calls

c) Starts a new thread

d) Ensures variable values are updated across all threads

Answer:

a) Prevents code execution in multiple threads simultaneously

Explanation:

The 'synchronized' keyword in Java is used to lock an object for any shared resource, preventing multiple threads from executing a block of code simultaneously.

33. What is the default value of an object reference declared as an instance variable?

a) undefined

b) 0

c) null

d) Throws an exception

Answer:

c) null

Explanation:

In Java, if an object reference is declared as an instance variable and is not initialized, its default value is null.

34. How is a constant declared in Java?

a) Using the 'const' keyword

b) Using the 'final' keyword

c) Using the 'constant' keyword

d) Using the 'immutable' keyword

Answer:

b) Using the 'final' keyword

Explanation:

In Java, constants are declared using the 'final' keyword, which indicates that the value cannot be changed once assigned.

35. What is an abstract class in Java?

a) A class that cannot be instantiated and may or may not include abstract methods

b) A class that supports multiple inheritance

c) A class with only abstract methods

d) A class that hides its implementation details

Answer:

a) A class that cannot be instantiated and may or may not include abstract methods

Explanation:

An abstract class in Java is a class that cannot be instantiated (you cannot create objects of an abstract class) and can include both abstract and non-abstract methods.

36. In Java, what is a constructor?

a) A method used to destroy objects

b) A static method that runs when a class is first loaded

c) A block of code used to initialize an object

d) A method that is called when an object is cloned

Answer:

c) A block of code used to initialize an object

Explanation:

A constructor in Java is a special block of code that is called when an instance of an object is created. It is used to initialize the object.

37. What does the 'break' keyword do in a loop?

a) Stops the loop and exits it immediately

b) Pauses the loop execution

c) Breaks the code execution for debugging

d) None of the above

Answer:

a) Stops the loop and exits it immediately

Explanation:

The 'break' keyword in Java is used to immediately exit a loop, regardless of the loop's condition.

38. Which of these is not a valid Java keyword?

a) transient

b) volatile

c) include

d) instanceof

Answer:

c) include

Explanation:

'include' is not a keyword in Java. Keywords like 'transient', 'volatile', and 'instanceof' have specific meanings and purposes in the language.

39. What is the use of the 'extends' keyword in Java?

a) To extend the functionality of a method

b) To inherit from a superclass

c) To extend an interface

d) To increase the size of a data type

Answer:

b) To inherit from a superclass

Explanation:

The 'extends' keyword in Java is used for inheritance. It indicates that a class is derived from another class, known as the superclass.

40. How are exceptions handled in Java?

a) Using 'try' and 'catch' blocks

b) Using 'throw' and 'throws' keywords

c) Both a) and b)

d) Java does not support exception handling

Answer:

c) Both a) and b)

Explanation:

In Java, exceptions are handled using 'try' and 'catch' blocks, along with the 'throw' and 'throws' keywords. 'try' and 'catch' manage the code that may throw an exception, while 'throw' and 'throws' are used to explicitly throw an exception.

41. Which of these is true about the 'Comparator' interface in Java?

a) It is used to compare elements within a collection

b) It is used to sort collections and arrays of objects

c) It provides multiple methods for comparison

d) Both a) and b)

Answer:

d) Both a) and b)

Explanation:

The 'Comparator' interface is used in Java to compare elements within a collection and to sort collections and arrays of objects.

42. What will happen if a 'throw' statement is executed in a try block without a corresponding catch block?

a) Compilation Error

b) The finally block will handle the exception

c) The method will terminate and the exception is handled by the caller

d) The program will continue execution after the finally block

Answer:

c) The method will terminate and the exception is handled by the caller

Explanation:

If a 'throw' statement in a try block doesn't have a corresponding catch block in the method, the method terminates and the exception is passed to the caller.

43. Which of these collection classes implements a dynamic array in Java?

a) HashSet

b) ArrayList

c) HashMap

d) LinkedList

Answer:

b) ArrayList

Explanation:

ArrayList in Java implements a dynamic array, allowing elements to be added or removed while maintaining an internal array.

44. What is the primary difference between the HashSet and TreeSet classes in Java collections?

a) HashSet is faster than TreeSet

b) TreeSet is unordered while HashSet is ordered

c) HashSet allows duplicate elements while TreeSet does not

d) TreeSet maintains elements in a sorted order

Answer:

d) TreeSet maintains elements in a sorted order

Explanation:

The primary difference is that TreeSet maintains its elements in a sorted order, whereas HashSet does not guarantee any order.

45. In Java, which exception is thrown when trying to access an index of an array which is out of bounds?

a) ArrayIndexOutOfBoundsException

b) IndexOutOfBoundsException

c) IllegalArgumentException

d) NoSuchMethodException

Answer:

a) ArrayIndexOutOfBoundsException

Explanation:

ArrayIndexOutOfBoundsException is thrown to indicate that an array has been accessed with an illegal index.

46. What does the Collections.synchronizedList method do?

a) Sorts the list

b) Reverses the list

c) Returns a synchronized (thread-safe) list backed by the specified list

d) Shuffles the list randomly

Answer:

c) Returns a synchronized (thread-safe) list backed by the specified list

Explanation:

Collections.synchronizedList method wraps a list with a synchronized (thread-safe) list to allow safe multi-threaded access.

47. When should you use a LinkedHashMap over a HashMap?

a) When you need to store key-value pairs in insertion order

b) When you need a performance boost

c) When you need to save memory

d) When you need to use keys as objects

Answer:

a) When you need to store key-value pairs in insertion order

Explanation:

LinkedHashMap maintains the insertion order of elements, unlike HashMap which does not guarantee any specific order of elements.

48. What is the result of adding a duplicate element to a Java Set?

a) The set ignores the duplicate element

b) The set replaces the existing element

c) The set throws an exception

d) The set adds the duplicate element

Answer:

a) The set ignores the duplicate element

Explanation:

A Set in Java does not allow duplicate elements, and adding a duplicate element has no effect.

49. Which method must be implemented when a class implements the Comparable interface?

a) compareTo(Object obj)

b) compare()

c) equals(Object obj)

d) hashCode()

Answer:

a) compareTo(Object obj)

Explanation:

The Comparable interface requires the implementation of the compareTo(Object obj) method to compare the current object with the specified object.

50. What is the primary purpose of the 'finally' block in Java exception handling?

a) To handle exceptions

b) To run code regardless of whether an exception occurs or not

c) To throw a new exception

d) To recover from exceptions

Answer:

b) To run code regardless of whether an exception occurs or not

Explanation:

The 'finally' block in Java is used to execute code regardless of whether an exception is thrown or caught, ensuring that specific code always runs.