Java8Sample1.java

//client creates list of Ints
List<Integer> listOfInts = new ArrayList<Integer>();
listOfInts.add(2);
listOfInts.add(3);
listOfInts.add(4);

//client does the filtering based on his logic
//let's say he wants to filter out even numbers
Iterator<Integer> itr = listOfInts.iterator();
while (itr.hasNext()) {
  Integer i = itr.next();
	if(i%2==0)
	  itr.remove();
}

//Client calls Vendor provided function
int result = MathUtility.sum(listOfInts);

//In the provided Vendor's MathUtility class
class MathUtility {
	public static int sum(List<Integer> list){
		//ability to add is only here
		int sum=0;
		for(Integer i: list){
				sum=sum+i;
		}
		return sum;
}