The Java Collections API's provide a set of classes and interfaces that makes it easier to handle collections of objects. In a sense Collection's works a bit like arrays, except their size can change dynamically, and they have more advanced behavior than arrays.

Rather than having to write your own collection classes, Java provides these ready-to-use collection classes. Most of the Java collections are located in the java.util package. Java also has a set of concurrent collections in the java.util.concurrent package.

Following thins comes under Collections API

    Overview of Interfaces
    Iterable
    Collection
    Generic Collections
    List
    Set
    SortedSet
    NavigableSet
    Map
    SortedMap
    NavigableMap
    Queue
    Deque
    Stack
    hashCode() and equals()
    Sorting

For more information, visit the following links:

http://www.roseindia.net/java/jdk6/

http://www.roseindia.net/javacodeexamples/index.shtml

http://www.devmanuals.com/tutorials/java/collections/