Which Java Collections Framework interface represents an ordered collection that allows duplicate elements and positional access via zero-based indexing?
Option A is correct. List (implemented by ArrayList, LinkedList, Vector) is an ordered collection that permits null and duplicate elements and provides index-based access.
Which implementation of Map interface in Java maintains elements in a sorted order based on their keys' natural ordering or a custom Comparator?
Option A is correct. TreeMap is a Red-Black tree-based NavigableMap implementation that keeps keys sorted in natural order or according to a Comparator provided at creation time.
What is the time complexity of element lookup (get) in a well-distributed HashMap in Java under optimal conditions?
Option C is correct. HashMap provides O(1) average constant time complexity for basic operations like get() and put(), assuming a uniform hash code distribution across bucket bins.
In Java Generics, what does the wildcard expression '<? extends Number>' specify?
Option A is correct. <? extends Number> is an upper-bounded wildcard that restricts the unknown type to be either Number or any subtype (e.g., Integer, Double, Float).
What process does the Java compiler perform during compilation regarding Generics to maintain backward compatibility with older JVM versions?
Option B is correct. Type Erasure removes all generic type parameters at compile-time and replaces them with their bounds or Object, generating raw bytecode for backward compatibility.