1. Which of these is not a Java keyword?
- a) abstract
- b) assert
- c) main
- d) volatile
Answer: C - "main" is not a Java keyword, though it's used as the method name where Java program execution begins.
2. What is the default value of a boolean variable in Java?
- a) true
- b) false
- c) null
- d) 0
Answer: B - The default value of a boolean variable in Java is false.
3. Which collection class implements a FIFO (first-in-first-out) behavior?
- a) ArrayList
- b) LinkedList
- c) PriorityQueue
- d) ArrayDeque
Answer: D - ArrayDeque can be used as a FIFO queue when using add() and remove() methods.
4. What is the size of 'int' data type in Java?
- a) 16 bits
- b) 32 bits
- c) 64 bits
- d) Platform dependent
Answer: B - In Java, int is always 32 bits regardless of the operating system or processor architecture.
5. Which method must be implemented by all threads in Java?
- a) start()
- b) init()
- c) run()
- d) execute()
Answer: C - The run() method must be implemented as it contains the code that constitutes the thread's task.
6. What is the superclass of all exception classes in Java?
- a) Error
- b) RuntimeException
- c) Throwable
- d) Exception
Answer: C - Throwable is the superclass of all errors and exceptions in Java.
7. Which of these is not a valid Java identifier?
- a) _variable
- b) $value
- c) 2ndPlace
- d) finalValue
Answer: C - Identifiers cannot start with a digit in Java.
8. What does the 'final' keyword indicate when applied to a method?
- a) The method cannot be overridden
- b) The method cannot throw exceptions
- c) The method must be implemented immediately
- d) The method cannot be accessed from other classes
Answer: A - A final method cannot be overridden by subclasses.
9. Which interface should be implemented for sorting objects of a class?
- a) Serializable
- b) Cloneable
- c) Comparable
- d) Runnable
Answer: C - The Comparable interface provides natural ordering for objects of a class.
10. What is the output of: System.out.println(5 + 3 + "Java");
- a) 8Java
- b) 53Java
- c) Compilation error
- d) Runtime error
Answer: A - The + operator performs addition first (5+3=8) then string concatenation.
11. Which of these is not a feature of Java?
- a) Platform independence
- b) Multiple inheritance
- c) Automatic garbage collection
- d) Strong type checking
Answer: B - Java doesn't support multiple inheritance of classes (though it supports multiple interface implementation).
12. What is the purpose of the 'static' keyword?
- a) To prevent method overriding
- b) To indicate class-level members
- c) To make variables constant
- d) To allow dynamic binding
Answer: B - The static keyword is used for class-level members that belong to the class rather than instances.
13. Which package is automatically imported in every Java program?
- a) java.util
- b) java.io
- c) java.lang
- d) java.awt
Answer: C - The java.lang package is automatically imported and contains fundamental classes.
14. What is the correct way to create an ArrayList that can store String objects?
- a) ArrayList
list = new ArrayList(); - b) ArrayList list = new ArrayList
(); - c) ArrayList
list = new ArrayList (); - d) Both A and C
Answer: D - Both syntaxes are correct in Java, though the diamond operator (<>) is preferred in newer versions.
15. Which of these is a checked exception?
- a) NullPointerException
- b) ArrayIndexOutOfBoundsException
- c) IOException
- d) ArithmeticException
Answer: C - IOException is a checked exception that must be either caught or declared in the method signature.
16. What is the output of: System.out.println(Math.floor(-7.4));
- a) -7
- b) -7.0
- c) -8
- d) -8.0
Answer: D - Math.floor() returns the largest double value that is less than or equal to the argument (-8.0 in this case).
17. Which access modifier provides the most restrictive access level?
- a) public
- b) protected
- c) default (no modifier)
- d) private
Answer: D - Private provides the most restrictive access, limiting visibility to the declaring class only.
18. What is the purpose of the 'transient' keyword?
- a) To indicate a variable should not be serialized
- b) To make a variable thread-safe
- c) To prevent method overriding
- d) To make a variable constant
Answer: A - The transient keyword indicates that a variable should not be included in serialization.
19. Which of these is not a valid Java comment?
- a) // Single-line comment
- b) /* Multi-line comment */
- c) /** Documentation comment */
- d)
Answer: D - HTML-style comments are not valid in Java source code.
20. What is the parent class of all Java classes?
- a) Object
- b) Class
- c) Root
- d) Super
Answer: A - The Object class is the superclass of all other classes in Java.