move datastructures into collections for organization

study/collections.MD

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+### Common Java Data Structures Summary
+
+Java contains many object based data structures that you can import, some used more than others (ArrayList, for example). 
+
+Not all of them work in familiar ways, and their methods can be confusing without proper usage, study, and a quick explanation over how they're used.
+
+#### Interfaces
+##### Collection
+
+Common Implementing SubInterfaces:
+* Deque
+* List
+* Queue
+* Set
+* SortedSet
+
+Common Implementing Classes: 
+* ArrayList
+* ArrayDeque
+* EnumSet
+* HashSet
+* LinkedList
+* PriorityQueue
+* Stack
+* TreeSet
+
+##### Iterable 
+
+Common Implementing SubInterfaces
+* Collection
+* Deque
+* List
+* Queue
+* Set
+* SortedSet
+
+Common Implementing Classes:
+* ArrayDeque
+* ArrayList
+* EnumSet
+* HashSet
+* LinkedList
+* PriorityQueue
+* Stack
+* TreeSet
+
+##### List
+
+Super Interfaces:
+* Collection
+* Iterable
+
+Implementing Classes:
+* ArrayList
+* LinkedList
+* Stack
+
+A unordered collection (also known as a *sequence*) that allows precise control over where each element is inserted in a list.
+
+Users have methods allowing all of the following to methods:
+* 4 methods providing positional index-based access to list elements.
+* 1 method for accessing a special iterator, `ListIterator` allowing element insertion and replacement starting from a specified position.
+* 2 methods for searching for a specified object. Usually *costly* linear searches.
+* 2 methods for efficiently inserting and removing *multiple* elements at an arbitrary point.
+
+##### Set
+##### Queue
+##### Deque
+##### SortedSet
+##### Map
+##### SortedMap
+##### NavigableMap
+
+#### Classes
+##### ArrayList
+##### LinkedList
+##### Stack
+##### PriorityQueue
+##### TreeSet
+##### ArrayDeque
+##### EnumSet
+##### HashSet
+##### HashMap