A collection is an object that contains a group of objects.
Each object in a collection is called an element. Every collection contains a group of objects.
Each different type of collection manages their elements in its own way.
The Collections Framework consists of interfaces, implementation classes, and some utility classes to handle most types of collections.
Java Collections are designed to work only with objects.
All collection classes in Java are declared generic.
The Java Collections Framework has three main components:
An interface in Java Collections Framework represents a specific type of collection.
For example, the
List interface represents a list.
Set interface represents a set.
Map interface represents a map.
The data structures defined by interfaces rather than a class has the following advantages: we can provide different implementation for the same interfaces.
The Java Collections Framework also provides implementations of collection interfaces.
We should always try to define the type of the class using interfaces, rather than using their implementation classes.
The following code shows how to use the implementation
ArrayList to create a list:
List<String> names = new ArrayList<>();
If possible we should avoid using the following way to create a list object.
ArrayList<String> names = new ArrayList<>();
We can perform different actions on a collection.