Discussion

Collections

Learning objectives

  • Know and use common methods in the Collections class
  • Use the Iterator interface to traverse the elements in a collection
  • Explore the relationship between interfaces and classes in Java

Java Arrays and Collections

Primitive Array - Core Java Type

Collection API - Lists, Sets, Queues

Generics and Typing Interfaces

Collection -Structure

LISTS

SETS

QUEUE

Collection Class

Collection Framework

What is a Collection?

  • A collection is a container object that holds a group of objects, often referred to as elements.
  • A List is an ordered collection that allows duplicate elements.
  • A Map stores key-value pairs, similar to a database table.
  • A Set or Map can be either sorted or unsorted.
  • Sorted collections guarantee iteration in a defined order, such as natural ordering or a comparator-defined order.
  • Unsorted collections do not provide any guarantee about iteration order.
  • Collections are dynamic and growable in nature.

Collection Framework

Collection Framework (Interface/Classes)

Interface

Implementations i.e . Classes

Algorithms

Java Arrays vs. Collections

Array Collection
Fixed size Dynamic and resizable
Holds only homogeneous data Can hold both homogeneous and heterogeneous data
Less memory-efficient compared to collections More memory-efficient due to dynamic allocation
No built-in data structures Uses built-in data structures and algorithms
Can store both primitive and object types Stores only object types

Collection vs. Collections

Collection Collections
Root interface of Java Collection Framework Utility class for collection operations
Implemented by List, Set, and Queue Provides utility methods like sort(), reverse(), shuffle(), etc.

What is a Data Structure?

A data structure is a way of organizing and storing data efficiently. It not only holds data but also provides operations for accessing, modifying, and managing it.

What is a Container?

A container is a class that holds and organizes objects, such as arrays and lists. Containers define both an organizing structure and an interface for interacting with the stored elements.

Array

ArrayList

  • Implements the List interface.
  • Creates an object array that dynamically grows as needed. It can hold null values.
  • Allows duplicate elements.
  • Developers can add or remove elements using index values.
  • The initial capacity can be set when the ArrayList is created.
  • ArrayList is a concrete class with a default initial capacity of ten.
  • ArrayList is faster for retrieving data but slower for modifications.

ArrayList Examples

List

  • The list interface is an ordered collection. Stores and access data in a sequential manner
  • It extends the Collection interface
  • List can include duplicate elements while sets cannot
  • Github code sample List

Linked List

  • LinkedList class can contain duplicate elements.
  • It also implements the Queue interface
  • LinkedList class can be used as list, stack or queue.
  • Github code sample Linked List

Linked List

  • Every nodes stores the data itself and a reference to next node
  • It needs more memory than arrays
  • It is a good choice for adding or removing elements from the list. It is slightly faster in a linked list.
  • There is no need for shifting items.
  • O(N) linear running time complexity
  • A linked list uses a data structure called a doubly linked list
  • A linked list is faster for manipulating data but slower for retrieval.

head node

next node

null

LinkedList VS ArrayList performance comparison

Vector

  • Vector use a simple one dimensional array.
  • Java keeps doubling the size of the one dimensional array.
  • Allows duplicate elements. Insertion order is preserved.
  • Github code Vector

Stacks

  • Similar to deck of cards,stack of plates
  • A stack uses a last in, first out order (LIFO)
  • Last item we inserted is the first item we take out
  • It is an abstract data type
  • pop(),push() and peek() are some methods
  • Modern programming language are stack-oriented

Stacks

Queues

  • Similar to waiting in line
  • It is abstract data type
  • It is ordered collection
  • A queue or FIFO (first in, first out)
  • Basic operations enqueue(),dequeue() and peek()
  • peek- get the item at the front of the queue, but don't remove it.
  • used in operating systems and thread management(multithreading).Thread are stored in queues

Queues

PriorityQueue

  • PriorityQueue class implements a priority queue
  • Orders its elements according to their natural ordering using Comparable
  • The element with the least value is assigned the highest priority and thus removed from the queue first.
  • If there are several elements with the same highest priority the tie is broken randomly.
  • peek() retrieves, but does not remove
  • pool() retrieves and remove the heaod of this queue or returns null if this queue is empty
  • Github code PriorityQueue

Deque

  • It is pronounce as deck
  • A deque is a double-ended queue that allows insertion and removal at either front or end
  • Offer FIFO or LIFO behavior.
  • Github code Deque

Thank you