http://zh.visualgo.net/
Note: 數據集合存儲結構，默認no synchronized，允許NULL，允許duplicate
Tree結構支持內部元素根據指定的規則排序

Collection
├List
│├LinkedList
│├ArrayList
│└Vector
│　└Stack
└Set
├HashSet
├TreeSet
Map
├Hashtable
├TreeMap
├HashMap
└WeakHashMap

Collection

List

• LinkedList

• 實現了List<E>, Deque<E>, Queue<E>
• List 【Every* element in the {@code List} has an index；allow duplicate* elements, as compared to Sets, where elements have to be unique】
• Deque 【double ended queue】【FIFO (First-In-First-Out) 】【Deques can also be used as LIFO (Last-In-First-Out) stacks】

注:push-pollLast 滿足LIFO
add-poll滿足FIFO

• you should probably use {@link ArrayList} if you don't need the queue-like behavior.

• ArrayList

ArrayList is an implementation of {@link List}, backed by an array.

• Vector

Vector is an implementation of {@link List}, backed by an array and synchronized.

• Stack

• {@code Stack} is a **Last-In/First-Out(LIFO) *data structure which represents a stack of objects.
• including null objects. There is no limit to the size of the stack.

Set

(A {@code Set} is a data structure which does not allow duplicate elements.)

• TreeSet

• 實現了SortedSet接口，支持元素排序

• HashSet

Map

A {@code Map} is a data structure consisting of a set of keys and values in which each key is mapped to a single value.

• HashTable

• Hashtable is a synchronized implementation of {@link Map}. All optional operations are supported.
• **Neither keys nor values can be null. *(Use {@code HashMap} or {@code LinkedHashMap} if you need null keys or values.)

• TreeMap

A map whose entries are sorted by their keys.

• HashMap

Note: the implementation of {@code HashMap} is not synchronized.

• WeakHashMap

WeakHashMap is an implementation of Map with keys which are WeakReferences.

• LinkedHashMap

doubly-linked list