Collections and Generics - SCJP Sun Certified Programmer for Java Platform SE6 - page 426

These objectives are Section 6 of the SCJP exam objectives.
The exam tests your knowledge of the Collections API,
including the use of generics. This chapter covers all of these
topics in detail.
Overview of Collections
A collection is a group of objects contained in a single element. Examples of collections
include an array of integers, a vector of strings, or a hash map of vehicles. The Java
Collections Framework is a unifi ed set of classes and interfaces defi ned in the java.util
package for storing collections. For the exam, you need to understand the different types
of collections in the Collections Framework, including lists, maps, and sets. You need
to recognize which collection to use given a specifi c scenario. The exam also tests your
knowledge of the Comparable interface and the difference between == and the equals
method. This section discusses all of these topics, starting with a discussion on the
collections interfaces, which provide the foundation of the Collections Framework.
The Collections Interfaces
The java.util package contains a group of interfaces referred to as the collections
interfaces to represent the various types of collections. The root interface of the collections
interfaces is Collection . There are different types of collections, and the subinterfaces of
Collection refl ect these various types of collections, as follows:
Lists A list is an ordered collection of elements that allows duplicate entries. Lists
implement the List interface, and elements in a list can be accessed by an integer index.
Sets A set is a collection that does not allow duplicate entries. Sets implement the Set
interface.
Queues A queue is a collection that orders its elements in a specifi c order for processing.
A typical queue processes its elements in a fi rst-in, fi rst-out (FIFO) fashion, but other
ordering is possible. Queues implement the Queue interface.
Maps A map is a collection that maps keys to values, with no duplicate keys allowed.
The elements in a map are key-value pairs. Maps implement the Map interface, which is
unique because the Map interface is not a subinterface of Collection like the other types of
collections.