Q1) The union of two collections consists of their contents combined into a new collection. Add method union to  interface BagInterface for ADT bag which returns as new bag the union of bag receiving call to method and bag which is the method's one argument.

Note that the union of two bags might contain duplicate items. For example, if object x occures five times in one bag and twice in another, the union of these bags contains x seven times. Specifically, suppose bag1 and bag2 are Bag objects, where Bag implements BagInterface; bag1 contains the String objects a, b,c; and bag2 contains the String objects b,b,d and e. After the statement

BagInterface everything = bag1.union(bag2); executes the bag and everything contains the strings a, b, b, b, c, d, and e.