Collection is defined as several things grouped together.
Java collection framework is made up of various interfaces to work with different groups. Implementation of the interfaces allow us to do our job but this means that data structure can be changed without changing the code.
Java.util package contains an interface called Collection. Collection is an interface which means it defines abstract methods (methods without body). The classes implementing this interface will define the implementation for the abstract methods in the Collection interface.
Following are the list of classes that implement Collection interface:
AbstractCollection, AbstractList, AbstractSet, ArrayList, BeanContextServicesSupport, BeanContextSupport, HashSet, LinkedHashSet, LinkedList, TreeSet, Vector