Collection is a root level interface of the Java Collection Framework. Most of the classes in
Java Collection Framework implements from this interface. List, Set and Queue are main
sub interfaces of this interface. JDK doesn’t provide any direct implementations of this
interface. But, JDK provides direct implementations of it’s sub interfaces. ArrayList, Vector,
HashSet, LinkedHashSet, PriorityQueue are some indirect implementations of Collection
interface. Map interface, which is also a part of java collection framework, doesn’t inherit
from Collection interface. Collection interface is a member of java.util package.
Collections is an utility class in java.util package. It consists of only static methods which are
used to operate on objects of type Collection. For example, it has the method to find the
maximum element in a collection, it has the method to sort the collection, it has the method
to search for a particular element in a collection. Below is the list of some important
methods of Collections class.