Collection 和 Collections 有什么区别?



 * The root interface in the <i>collection hierarchy</i>.  A collection
 * represents a group of objects, known as its <i>elements</i>.  Some
 * collections allow duplicate elements and others do not.  Some are ordered
 * and others unordered.  The JDK does not provide any <i>direct</i>
 * implementations of this interface: it provides implementations of more
 * specific subinterfaces like <tt>Set</tt> and <tt>List</tt>.  This interface
 * is typically used to pass collections around and manipulate them where
 * maximum generality is desired.



* This class consists exclusively of static methods that operate on or return
* collections.  It contains polymorphic algorithms that operate on
* collections, "wrappers", which return a new collection backed by a
* specified collection, and a few other odds and ends.



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