Hi,

Here is the answer.

A Collection(in the API reference documentation)represents a group of objects, known as its elements. The primary use of the Collection interface is to pass around collections of objects where maximum generality is desired.

For example,

by convention all general-purpose collection implementations (which typically implement some subinterface of Collection like Set or List) have a constructor that takes a Collection argument. This constructor initializes the new Collection to contain all of the elements in the specified Collection. This constructor allows the caller to create a Collection of a desired implementation type, initially containing all of the elements in any given Collection, whatever its subinterface or implementation type. Suppose you have a Collection, c, which may be a List, a Set, or some other kind of Collection.

Thanks.