Java8Samples6.java

//Vendor code

static class IntegerAddition implements BinaryOperator<Integer> {

	static private IntegerAddition instance = new IntegerAddition() ;
	private IntegerAddition() {}
	
	@Override
	public Integer apply(Integer t, Integer u) {
		return t + u;
	}

	public static IntegerAddition instance() {
		return instance;
	}
}

	
public static <T extends Number> Optional<T> sum(List<T> list, Predicate<T> condition, BinaryOperator<T> operation){
		return list.parallelStream()
		.filter(condition)
		.map(i -> i)
    .reduce(operation);
}


//client
int result = MathUtility.sum(listOfInts, i->i<4, MathUtility.IntegerAddition.instance()).get();