11.) What is the time complexity for retrieving a value by key in a HashMap?
12.) Which interface provides the basic functionality for all collections in the Java Collections Framework?
13.) What is the main purpose of the Iterator interface in Java?
14.) Which collection allows elements to be stored in a key-value pair format?
15.) Which collection allows elements to be stored in an ordered sequence, and elements can be accessed by their index?
16.) Which collection allows elements to be stored in a sorted order?
17.) What is the purpose of the Comparator interface in Java?
18.) Which Java collection is typically used to implement a queue data structure?
19.) Which Java collection is typically used to implement a priority queue data structure?
20.) Which Java collection allows elements to be retrieved in a last-in-first-out (LIFO) order?