What design pattern guarantees that a class has only one instance and provides a global point of access to that instance in Java?
Option C is correct. The Singleton pattern restricts class instantiation to a single object, using a private constructor and a public static getter method.
Introduced in Java 14/16, what restricted class type is designed to act as transparent, immutable data carriers with auto-generated getters, equals(), hashCode(), and toString()?
Option B is correct. Java Records (record Point(int x, int y) {}) provide compact syntax for creating immutable data-transfer objects without boilerplate code.
In Java 17, which keyword is used to restrict which other classes or interfaces may extend or implement a class?
Option B is correct. A 'sealed' class or interface restricts subclassing by specifying permitted subtypes using the 'permits' clause (e.g., public sealed class Shape permits Circle, Square).
Which java.util Collection interface does NOT allow duplicate elements and models the mathematical set abstraction?
Option C is correct. Set is a collection that contains no duplicate elements (at most one null element) and enforces uniqueness.
Which collection implementation in java.util provides a thread-safe variant of ArrayList where all mutative operations (add, set) are implemented by making a fresh copy?
Option B is correct. CopyOnWriteArrayList creates a underlying array copy on write operations, making read operations fast and thread-safe without synchronization overhead.