1. 14.1 The java.util Package

2. 14.1.1 The java.util package Predefined utility classes to:
Manage collections of objects
Manage communication between objects
Manipulate information within objects

3. 14.2.1 Understanding collections
Collections are objects that reference a group of objects
Unlike arrays, collections can only reference the Object data type
This means that any object can be stored in a collection, but casting is required to retrieve the object
Collections can:
Change size
Provide sorting
Support adding and deleting elements

4. 14.2.2 Collection storage technologies
Array:
Fixed size, fast & efficient to access, difficult to modify
Linked List:
Elements have references to the preceeding and following element, easy to change, slow to search
Tree:
Easy to change, stores elements in order
Hashtable:
Uses an indexing key to identify elements. Elements are retrieved from the hashtable using the element’s key

5. 14.2.4 Types of collections Collection List Set Map
Simple container of unordered objects. Duplicates are permitted
List
Container of ordered elements. Duplicates are permitted
Set
Unordered collection of objects in which duplicates are not permitted
Map
Collection of key/value pairs. The key is used to index the element. Duplicate keys are not permitted

6. 14.3.2 Collection interfaces
Defines behavior of collection objects
Hierarchy of six interfaces

7. Collection classes

8. Set objects
HashSet implements the Set interface. Duplicates are not permitted
TreeSet implements OrderedSet. Includes methods to take advantage of the ordering, eg:
TreeSet.first()
TreeSet.last()
TreeSet.headSet()
TreeSet.subSet()

9. 14.3.5 List objects Vector ArrayList LinkedList
A collection of objects. Implements the List interface. Grows as necessary. Retains the order in which the objects were added
ArrayList
Resizable, ordered array
LinkedList
Each element has a reference to the preceeding and following element

10. 14.3.6 Map objects Use a unique key to reference the element
Key determines where the element is stored
The hashCode() method of the Object class can be overridden to provide unique keys

11. 14.3.7 Iterators Provide a method for stepping through collections
Iterating through a set is non-deterministic
Use the ListIterator class for iterating through lists

12. 14.3.8 Sorting and shuffling list objects
Collection has methods for sorting
Collection.sort() sorts the entire list or a subsection
Collection.reverse() reverses the current list
Shuffling moves elements within the list
Collection.shuffle()
Collection.shuffle(Random r)