50 Java Interview Question and Answer |

1. Question: What is Java?

• A) A scripting language
• B) A programming language
• C) A markup language
• D) An operating system
• Answer: B) A programming language

1. Question: What is the JVM?

• A) Java Virtual Machine
• B) Java Variable Manager
• C) Java Version Manager
• D) Java Visual Model
• Answer: A) Java Virtual Machine

1. Question: Which keyword is used to define a class in Java?

• A) class
• B) Class
• C) Class
• D) category
• Answer: A) class

1. Question: What is the purpose of the ‘static’ keyword in Java?

• A) To define a constant
• B) To specify a method or variable as class-level
• C) To prevent inheritance
• D) To declare a method as private
• Answer: B) To specify a method or variable as class-level

1. Question: Which of the following is NOT a primitive data type in Java?

• A) int
• B) float
• C) string
• D) char
• Answer: C) string

1. Question: What is the output of the following code snippet?

String str = "Hello";
str = str + " World!";
System.out.println(str);

• A) Hello World!
• B) Hello
• C) World!
• D) Compilation Error
• Answer: A) Hello World!

1. Question: What is the default value of an integer variable in Java?

• A) 0
• B) 1
• C) -1
• D) null
• Answer: A) 0

1. Question: Which keyword is used to instantiate an object in Java?

• A) instantiate
• B) new
• C) create
• D) alloc
• Answer: B) new

1. Question: What is the difference between ‘==’ and ‘.equals()’ in Java?

• A) They are interchangeable
• B) ‘==’ compares object references, ‘.equals()’ compares object contents
• C) ‘.equals()’ compares object references, ‘==’ compares object contents
• D) Both do the same thing
• Answer: B) ‘==’ compares object references, ‘.equals()’ compares object contents

1. Question: Which of the following is NOT a valid Java identifier?
   • A) myVar
   • B) 123var
   • C) _myVar
   • D) $myVar
   • Answer: B) 123var
2. Question: What is method overloading in Java?
   • A) Creating multiple methods with the same name but different parameters
   • B) Creating multiple methods with the same name and same parameters
   • C) Creating multiple methods with different names but the same parameters
   • D) Creating multiple methods with different return types
   • Answer: A) Creating multiple methods with the same name but different parameters
3. Question: What is method overriding in Java?
   • A) Creating multiple methods with the same name but different parameters
   • B) Creating multiple methods with the same name and same parameters
   • C) Creating multiple methods with different names but the same parameters
   • D) Redefining a method in a subclass with the same signature as a method in the superclass
   • Answer: D) Redefining a method in a subclass with the same signature as a method in the superclass
4. Question: What is the purpose of the ‘final’ keyword in Java?
   • A) To prevent a class from being extended
   • B) To prevent a method from being overridden
   • C) To prevent a variable from being modified
   • D) All of the above
   • Answer: D) All of the above
5. Question: What is an abstract class in Java?
   • A) A class with only abstract methods
   • B) A class that cannot be instantiated
   • C) A class that can be extended but not instantiated
   • D) A class with no methods
   • Answer: C) A class that can be extended but not instantiated
6. Question: What is an interface in Java?
   • A) A class with only abstract methods
   • B) A class that cannot be instantiated
   • C) A class that can be extended but not instantiated
   • D) A blueprint of a class that can be implemented by other classes
   • Answer: D) A blueprint of a class that can be implemented by other classes
7. Question: What is the purpose of the ‘this’ keyword in Java?
   • A) To refer to the current class instance variable
   • B) To create a new instance of a class
   • C) To refer to the superclass
   • D) To refer to the current class method
   • Answer: A) To refer to the current class instance variable
8. Question: What is the purpose of the ‘super’ keyword in Java?
   • A) To refer to the current class instance variable
   • B) To create a new instance of a class
   • C) To refer to the superclass
   • D) To refer to the current class method
   • Answer: C) To refer to the superclass
9. Question: What is the purpose of the ‘throw’ keyword in Java?
   • A) To declare a variable
   • B) To create a new instance of an object
   • C) To explicitly throw an exception
   • D) To catch an exception
   • Answer: C) To explicitly throw an exception
10. Question: What is the purpose of the ‘throws’ keyword in Java?
    • A) To declare a variable
    • B) To create a new instance of an object
    • C) To explicitly throw an exception
    • D) To declare that a method may throw an exception
    • Answer: D) To declare that a method may throw an exception
11. Question: What is a constructor in Java?
    • A) A method that has no return type
    • B) A method that is called when an object is instantiated
    • C) A method that is called when an object is destroyed
    • D) A method that has the same name as the class
    • Answer: B) A method that is called when an object is instantiated
12. Question: What is the purpose of the ‘finalize’ method in Java?
    • A) To initialize an object
    • B) To de-initialize an object
    • C) To clean up resources before an object is garbage collected
    • D) To catch exceptions
    • Answer: C) To clean up resources before an object is garbage collected

22.

Question: What is the purpose of the ‘static’ block in Java?
– A) To initialize static variables
– B) To initialize instance variables
– C) To define static methods
– D) To define instance methods
– Answer: A) To initialize static variables

23. Question: What is the purpose of the ‘transient’ keyword in Java?
    • A) To prevent serialization of a variable
    • B) To allow serialization of a variable
    • C) To prevent a class from being serialized
    • D) To allow a class to be serialized
    • Answer: A) To prevent serialization of a variable
24. Question: What is the purpose of the ‘volatile’ keyword in Java?
    • A) To prevent multiple threads from accessing a variable at the same time
    • B) To ensure that changes to a variable are immediately visible to other threads
    • C) To prevent a variable from being modified
    • D) To ensure that a variable is initialized before it is accessed
    • Answer: B) To ensure that changes to a variable are immediately visible to other threads
25. Question: What is the purpose of the ‘synchronized’ keyword in Java?
    • A) To prevent multiple threads from accessing a variable at the same time
    • B) To ensure that changes to a variable are immediately visible to other threads
    • C) To prevent a variable from being modified
    • D) To ensure that a variable is initialized before it is accessed
    • Answer: A) To prevent multiple threads from accessing a variable at the same time
26. Question: What is a thread in Java?
    • A) A process
    • B) A lightweight process
    • C) A class
    • D) A variable
    • Answer: B) A lightweight process
27. Question: What is the purpose of the ‘start()’ method in Java threads?
    • A) To start a new thread
    • B) To stop a thread
    • C) To pause a thread
    • D) To resume a thread
    • Answer: A) To start a new thread
28. Question: What is the purpose of the ‘sleep()’ method in Java threads?
    • A) To start a new thread
    • B) To stop a thread
    • C) To pause a thread
    • D) To resume a thread
    • Answer: C) To pause a thread
29. Question: What is the purpose of the ‘yield()’ method in Java threads?
    • A) To start a new thread
    • B) To stop a thread
    • C) To pause a thread
    • D) To give up the CPU temporarily
    • Answer: D) To give up the CPU temporarily
30. Question: What is the purpose of the ‘join()’ method in Java threads?
    • A) To start a new thread
    • B) To stop a thread
    • C) To pause a thread
    • D) To wait for a thread to finish
    • Answer: D) To wait for a thread to finish
31. Question: What is the purpose of the ‘notify()’ method in Java threads?
    • A) To wake up a single waiting thread
    • B) To wake up all waiting threads
    • C) To put a thread to sleep
    • D) To stop a thread
    • Answer: A) To wake up a single waiting thread
32. Question: What is the purpose of the ‘notifyAll()’ method in Java threads?
    • A) To wake up a single waiting thread
    • B) To wake up all waiting threads
    • C) To put a thread to sleep
    • D) To stop a thread
    • Answer: B) To wake up all waiting threads
33. Question: What is the purpose of the ‘wait()’ method in Java threads?
    • A) To wake up a single waiting thread
    • B) To wake up all waiting threads
    • C) To put a thread to sleep
    • D) To stop a thread
    • Answer: C) To put a thread to sleep
34. Question: What is the purpose of the ‘interrupt()’ method in Java threads?
    • A) To wake up a single waiting thread
    • B) To wake up all waiting threads
    • C) To put a thread to sleep
    • D) To stop a thread
    • Answer: D) To stop a thread
35. Question: What is the purpose of the ‘isAlive()’ method in Java threads?
    • A) To check if a thread is running
    • B) To check if a thread is paused
    • C) To check if a thread is sleeping
    • D) To check if a thread is terminated
    • Answer: A) To check if a thread is running
36. Question: What is the purpose of the ‘isInterrupted()’ method in Java threads?
    • A) To check if a thread is running
    • B) To check if a thread is paused
    • C) To check if a thread is sleeping
    • D) To check if a thread has been interrupted
    • Answer: D) To check if a thread has been interrupted
37. Question: What is the purpose of the ‘getName()’ method in Java threads?
    • A) To get the name of a thread
    • B) To set the name of a thread
    • C) To get the ID of a thread
    • D) To set the priority of a thread
    • Answer: A) To get the name of a thread
38. Question: What is the purpose of the ‘setName()’ method in Java threads?
    • A) To get the name of a thread
    • B) To set the name of a thread
    • C) To get the ID of a thread
    • D) To set the priority of a thread
    • Answer: B) To set the name of a thread
39. Question: What is the purpose of the ‘getPriority()’ method in Java threads?
    • A) To get the name of a thread
    • B) To set the name of a thread
    • C) To get the ID of a thread
    • D) To get the priority of a thread
    • Answer: D) To get the priority of a thread
40. Question: What is the purpose of the ‘setPriority()’ method in Java threads?
    • A) To get the name of a thread
    • B) To set the name of a thread
    • C) To get the ID of a thread
    • D) To set the priority of a thread
    • Answer: D) To set the priority of a thread
41. Question: What is the purpose of the ‘yield()’ method in Java threads?
    • A) To give up the CPU temporarily
    • B) To give up the CPU permanently
    • C) To wait for a thread to finish
    • D) To wake up a waiting thread
    • Answer: A) To give up the CPU temporarily
42. Question: What is the purpose of the ‘sleep()’ method in Java threads?
    • A) To give up the CPU temporarily
    • B) To give up the CPU permanently
    • C) To wait for a thread to finish
    • D) To wake up a waiting thread
    • Answer: C) To wait for a thread to finish
43. Question: What is the purpose of the ‘join()’ method in Java threads?
    • A) To give up the CPU temporarily
    • B) To give up the CPU permanently
    • C) To wait for a thread to finish
    • D) To wake up a waiting thread
    • Answer: C) To wait for a thread to finish
44. Question: What is the purpose of the ‘notify()’ method in Java threads?
    • A) To give up the CPU temporarily
    • B) To give up the CPU permanently
    • C) To wake up a waiting thread
    • D) To put a thread to sleep
    • Answer: C) To wake up a waiting thread
45. Question: What is the purpose of the ‘notifyAll()’ method in Java threads?
    • A) To give up the CPU temporarily
    • B) To give up the CPU permanently
    • C) To wake up all waiting threads
    • D) To put a thread to sleep
    • Answer: C) To wake up all waiting threads
46. Question: What is the purpose of the ‘interrupt()’ method in Java threads?
    • A) To give up the CPU temporarily
    • B) To give up the CPU permanently
    • C) To stop a thread
    • D) To put a thread to sleep
    • Answer: C) To stop a thread
47. Question: What is the purpose of the ‘yield()’ method in Java threads?
    • A) To give up the CPU temporarily
    • B) To give up the CPU permanently
    • C) To stop a thread
    • D) To wake up a waiting thread
    • Answer: A) To give up the CPU temporarily
48. Question: What is the purpose of the ‘sleep()’ method in Java threads?
    • A) To give up the CPU temporarily
    • B) To give up the CPU permanently
    • C) To stop a thread
    • D) To wait for a thread to finish
    • Answer: A) To give up the CPU temporarily
49. Question: What is the purpose of the ‘join()’ method in Java threads?
    • A) To give up the CPU temporarily
    • B) To give up the CPU permanently
    • C) To stop a thread
    • D) To wait for a thread to finish
    • Answer: D) To wait for a thread to finish
50. Question: What is the purpose of the ‘notify()’ method in Java threads?
    • A) To give up the CPU temporarily
    • B) To give up the CPU permanently
    • C) To wake up a waiting thread
    • D) To stop a thread
    • Answer: C) To wake up a waiting thread

These questions cover a broad range of topics related to Java programming and multithreading. They can help assess a candidate’s understanding and proficiency in Java development.