Java Collections Overview

Collections are predefined set of classes or data structures which can be used to store the group or collections of objects. Unlike arrays, these data structures are powerful and can easily grow or shrink with out having to redefine them. The capacity planning and predefined algorithms for sort, search and manipulation make them easy to use.

There are primarily three types of Collections. They are List, Set and Map.

• List is used to store the elements in an order. The elements are stored in the order they are added and they can retrieved in the same order. List allows duplicate elements. Famous classes which implement List are Java ArrayList, Java LinkedList .

• Set stores only the unique elements. It is unordered and unique, so if we add any duplicate elements, it will only store one element. Famous classes which implement Set are HashSet Class In Java and Java TreeSet - TreeSet Examples in Java.

• Map is used to store key value pairs. In any map, the keys are unique, where as the values are non unique. Classes which implement Map are Java HashMap Implementation and TreeMap In Java - java.util.TreeMap.

We will discuss more details about the Collections in the next topics. There are lot of interesting programs to be written as well.