CSC/ECE 517 Fall 2011/ch1 1b ds

Cover the history of Collections frameworks back to the late 1970s or early 1980s, and how they were retrofitted to various languages. Discuss the advantage of a standard Collections framework (e.g., Java) vs. several competing frameworks (e.g., C++), and the advantage of collections built into the language (e.g., Ruby) vs. collections as class libraries. Give examples to illustrate the advantages you identify.

Authors

• Dilip Devaraj
• Srinath Sridhar

Java Collections Framework (JCF)

Java Collections Framework— is a library of classes that implement collections. The collections framework also provides utility methods to perform functions such as sorting a list of data. If you need to store instances of your own class in some types of collection then we need to employ hashing by writing our own hashCode and equals method.

The collections in Java are mainly the following List, Set, Map and Queue. Java provides these collections as interfaces from which one can write their own classes or can use the inbuilt Java classes that implement these interfaces.

List

List is a collection of objects that has a fixed order (when we add an object to the list, it will stay in the place we put it), and allows objects to be referred to by position.Duplicate elements are allowed in a list. The general-purpose List implementations are ArrayList and LinkedList. List<String> myList = new ArrayList<String>();

Set

A Set is a Collection that cannot contain duplicate elements. It models the mathematical set abstraction.The Java platform contains three general-purpose Set implementations: HashSet, TreeSet, and LinkedHashSet.

Map

A Map is an object that maps keys to values. A map cannot contain duplicate keys: Each key can map to at most one value. Maps are defined by the java.util.Map interface in Java. The three general-purpose Map implementations are HashMap, TreeMap and LinkedHashMap. The java.util.Map interface is extended by its subinterface, java.util.SortedMap. This interface defines a map that's sorted by the keys provided.

Queue

A Queue is a collection for holding elements prior to processing. Besides basic Collection operations, queues provide additional insertion, removal, and inspection operations. LinkedList implements the Queue interface, providing first in, first out (FIFO) queue operations.