Govt. Exams
Entrance Exams
Dequeue() throws InvalidOperationException on empty queue. TryDequeue() returns false instead. Peek() also throws but doesn't remove.
List<T> maintains insertion order and allows duplicates. HashSet<T> doesn't allow duplicates, SortedSet<T> sorts elements, and Queue<T> follows FIFO.
List nums = new List {1, 2, 3};
nums.Add(4);
Console.WriteLine(nums.Count);
The list initially has 3 elements. After Add(4), it has 4 elements. Count returns 4.
Stack<T> follows LIFO where the last element added is the first to be removed. Queue<T> follows FIFO (First In First Out).
Count returns the number of elements currently stored. Capacity is different and refers to allocated space.
List<T> allows duplicates as it stores elements sequentially. Dictionary and Hashtable enforce unique keys; attempting to add a duplicate key throws an exception.
List<T> is generic and type-safe, preventing boxing/unboxing overhead and providing compile-time type checking. ArrayList stores objects and requires casting.
System.Collections.Generic is the standard namespace for generic collections in C#. It provides type-safe collections that prevent runtime errors.
Abstract classes in C# cannot be instantiated directly. The compiler enforces this rule at compile-time. Abstract classes serve as blueprints and must be inherited by concrete classes that provide implementations for all abstract members. This ensures proper design and forces derived classes to implement required functionality.
Abstract methods have no implementation in the abstract class and force derived classes to provide their own implementation. They cannot be private as they must be overridable.
