How check if the lists in a list are not empty?

Question

I have a list of lists in Java. Here is the code:

List<List<Integer>> myList = new ArrayList<>();
myList.add(new ArrayList<Integer>());
myList.add(new ArrayList<Integer>());
myList.add(new ArrayList<Integer>());

myList.get(0).add(1);
myList.get(0).add(2);
myList.get(0).add(3);
myList.get(1).add(4);
myList.get(1).add(5);
myList.get(1).add(6);
myList.get(2).add(7);
myList.get(2).add(8);
myList.get(2).add(9);

Now in a part of my code I want to check if all three lists that are located in myList are not empty and null. Should I check each of these lists one by one, like this:

if (myList.get(0) != null && !myList.get(0).isEmpty()) { 
    // do something
} 

...or is there a better and shorter way to do instead of checking one by one?

Answer 1

You can use stream API for this, but also a plain loop too:

 boolean allNonEmptyOrNull = myList.stream()
     .allMatch(x -> x != null && !x.isEmpty());

Or you can check if null is contained or an an empty List for example, via:

System.out.println(myList.contains(null) || myList.contains(Collections.<Integer> emptyList()));

But this last option will break with Java 9 immutable collections, for example:

List.of(1, 2, 3).contains(null); 

will throw a NullPointerException.