Example of using stream flatMap function

StreamFlatMapExample.java

	// list of negative number
	List<Integer> negList = Arrays.asList(-4, -3, -2, -1);

	// list of positive number
	List<Integer> posList = Arrays.asList(1, 2, 3, 4);

	// find the odd number in both lists with single stream operation
	List<Integer> collector = Stream.of(negList, posList)
	      .flatMap(List::stream) //transform into stream of other objects
	      .filter(i -> i % 2 != 0)
	      .collect(Collectors.toList());
	System.out.println(collector);
	//Output: [-3, -1, 1, 3]