The java.util.Collections class contains static methods that operate on or return collections.
It has following characteristic.
It contains polymorphic algorithms that operate on collections,
"wrappers", which return a new collection backed by a specified collection.
The methods of this class all throw a NullPointerException if the collections or class objects provided to them are null.
- Collections is a member of the Java Collection Framework.
- Collections API
Learn Java Collection by Example