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web.groovymark@gmail.com
- December 26, 2024
Question 41
Which of the following is a valid way to create an immutable class?
- A. By declaring all fields as final
- B. By providing no setter methods
- C. By making the class final
- D. All of the above
Answer: D
Explanation: All the options contribute to creating an immutable class.
Question 42
How do you create a synchronized block in Java?
- A. synchronized void myMethod() {}
- B. synchronized (object) {}
- C. synchronized {}
- D. Both A and B
Answer: D
Explanation: Both synchronized void myMethod() {} and synchronized (object) {} create synchronized blocks.
Question 43
What does the instanceof keyword do in Java?
- A. Checks if an object is an instance of a class
- B. Compares two objects
- C. Casts an object to a class
- D. Creates a new instance
Answer: A
Explanation: The instanceof keyword checks if an object is an instance of a specified class.
Question 44
Which method is used to remove all elements from a List in Java?
- A. clear()
- B. removeAll()
- C. delete()
- D. empty()
Answer: A
Explanation: The clear() method is used to remove all elements from a List.
Question 45
What is the output of System.out.println(“Hello” + 5 + 2);?
- A. 7
- B. Hello7
- C. Hello52
- D. Error
Answer: C
Explanation: The expression evaluates to "Hello52" due to string concatenation.
Question 46
Which of the following is a valid way to declare a map in Java?
- A. Map<int, String> map = new HashMap<>();
- B. Map<String, String> map = new HashMap<>();
- C. Map<String, int> map = new HashMap<>();
- D. Map<String> map = new HashMap<String>();
Answer: B
Explanation: The correct syntax to declare a map is Map<String, String> map = new HashMap<>();.
Question 47
What is the purpose of the synchronized keyword in Java?
- A. To allow only one thread to access a method
- B. To declare a method as final
- C. To stop a thread
- D. To create a new thread
Answer: A
Explanation: The synchronized keyword is used to ensure that only one thread can access a method at a time.
Question 48
How do you check if a List contains a specific element in Java?
- A. list.includes(element);
- B. list.contains(element);
- C. list.has(element);
- D. list.indexOf(element);
Answer: B
Explanation: The contains() method is used to check if a List contains a specific element.
Question 49
What will the following code output? System.out.println(1 + “2” + 3);?
- A. 6
- B. 123
- C. 32
- D. 12
Answer: B
Explanation: The expression evaluates to "123" due to string concatenation.
Question 50
Which of the following is true about Java exceptions?
- A. All exceptions must be caught.
- B. Exceptions can be ignored.
- C. Only runtime exceptions must be caught.
- D. All exceptions must be handled.
Answer: C
Explanation: Only runtime exceptions do not need to be explicitly caught or declared.
