HashSet Implementation in Java

HashSet Implementation

HashSet Class Hierarchy

• HashSet implements the Set interface
• HashSet is a subclass of AbstractSet
• HashSet uses a HashMap instance to store its elements

HashSet Internal Workings

• Uses a HashMap to store elements, with the element as the key and a dummy object as the value
• The HashMap uses a hash table for storage, with chaining for collision resolution
• The hashCode() method of the elements is used to determine the index in the hash table

HashSet Operations

• Add: Adding an element involves putting the element as the key and a dummy object as the value in the underlying HashMap
• Remove: Removing an element involves removing the entry from the underlying HashMap
• Contains: Checking if an element is present involves checking if the HashMap contains the element as a key

HashSet Properties

• No duplicate elements: Since HashSet uses a HashMap internally, it does not allow duplicate elements
• No particular order: The order of elements in a HashSet is not guaranteed
• Null elements: HashSet allows null elements, but only one null element is allowed since it uses a HashMap internally

HashSet Class Hierarchy

• Implements the Set interface
• Subclass of AbstractSet

HashSet Internal Workings

• Uses a HashMap instance to store elements, with elements as keys and a dummy object as values
• HashMap uses a hash table for storage with chaining for collision resolution
• hashCode() method of elements determines index in the hash table

HashSet Operations

• Adding an element: element is put as key and a dummy object as value in underlying HashMap
• Removing an element: removing the entry from underlying HashMap
• Checking if an element is present: checking if HashMap contains the element as a key

HashSet Properties

• No duplicate elements due to internal HashMap
• No particular order of elements
• Allows null elements, but only one null element due to internal HashMap

Stack Operations

• A stack is a Last-In-First-Out (LIFO) data structure, where the last element added is the first one to be removed.
• Four common stack operations:
  • Push: adds an element to the top of the stack.
  • Pop: removes the top element from the stack.
  • Peek or Top: returns the top element of the stack without removing it.
  • IsEmpty: checks if the stack is empty.

Queue Operations

• A queue is a First-In-First-Out (FIFO) data structure, where the first element added is the first one to be removed.
• Four common queue operations:
  • Enqueue: adds an element to the end of the queue.
  • Dequeue: removes the front element from the queue.
  • Peek or Front: returns the front element of the queue without removing it.
  • IsEmpty: checks if the queue is empty.

Array Implementation

• Stacks and queues can be implemented using an array.
• The array size is fixed, and a pointer (or index) is used to keep track of the top or front element.
• Advantages of array implementation:
  • Fast access and manipulation of elements.
  • Efficient use of memory.
• Disadvantages of array implementation:
  • Fixed size, which can lead to overflow or underflow errors.
  • Resizing the array can be costly.

Linked List Implementation

• Stacks and queues can be implemented using a linked list.
• Each element is a separate node, and each node points to the next node in the list.
• Advantages of linked list implementation:
  • Dynamic size, which can grow or shrink as needed.
  • No risk of overflow or underflow errors.
• Disadvantages of linked list implementation:
  • Slower access and manipulation of elements compared to arrays.
  • More memory is required due to the overhead of node pointers.