Different Data Structures

collection

• Root interface for most collections

• Stores groups of objects

• Parent of List, Set, and Queue

• Does NOT include Maps

list

• Interface

• Ordered collection

• Allows duplicates

• Access by index

Implementations

• ArrayList

• LinkedList

• Vector

set

• Interface

• No duplicate elements

• No index

Implementations

• HashSet

• LinkedHashSet

• TreeSet

queue

• Interface

• FIFO (First In First Out)

Implementations

• LinkedList

• PriorityQueue

map

• Interface

• Stores key-value pairs

• Keys must be unique

• NOT part of the Collection interface

Implementations

• HashMap

• LinkedHashMap

• TreeMap

arraylist

• Class

• Implements List

• keeps elemements in order you added

• Allows duplicates

• Fast random access

• Slower insert/remove

linkedlist

• Class

• Implements List and Queue

• Ordered

• Allows duplicates

• Fast insertion/removal

• Slower random access

vector

• Class

• Like ArrayList

• Thread-safe (synchronized)

• Usually slower than ArrayList

stack

• Class

• Extends Vector

• LIFO

Methods

push()

pop()

peek()

hashset

• Class

• Implements Set

• No duplicates

• No ordering

• Fast

linkedhashset

• Class

• Implements Set

• No duplicates

• Keeps insertion order

treeset

• Class

• Implements NavigableSet (which extends SortedSet and Set)

• No duplicates

• Automatically sorted

hashmap

• Class

• Implements Map

• Key-value pairs

• Keys unique

• No ordering

linkedhashmap

• Class

• Implements Map

• Keeps insertion order

treemap

• Class

• Implements NavigableMap (which extends SortedMap and Map)

• Keys automatically sorted

comparable

• Interface

• Defines natural ordering

• Uses compareTo()

• comes with the class (default order)

comparator

• Interface

• Defines custom ordering

• Uses compare()

• compare differently (custom order)

iterator

Used to move through collections.

methods

hasNext()

next()

remove()

collectioons

Utility class with static methods

sort()

shuffle()

reverse()

binarySearch()

max()

min()