How to compare equality of lists of arrays with modern Java?

Question

I have two lists of arrays.

How do I easily compare equality of these with Java 8 and its features, without using external libraries? I am looking for a "better" (higher-level, shorter, more efficient) solution than brute-force code like this (untested code, may contain typos etc, not the point of the question):

boolean compare(List<String[]> list1, List<String[]> list2)  {     // tests for nulls etc omitted     if(list1.size() != list2.size()) {        return false;     }     for(i=0; i<list1.size(); ++i) {         if(!Arrays.equals(list1.get(i), list2.get(i))) {             return false;         }     }     return true; } 

Or, if there isn't any nicer way, that's a valid answer too.

Bonus: If Java 9 offers an even better way what whaterver Java 8 can offer, feel free to mention it as well.

Edit: After looking at the comments, and seeing how this question has become moderately hot, I think the "better" should include first checking lengths of all arrays, before checking array contents, because that has potential to find inequality much quicker, if inner arrays are long.

Answer 1

The for loop at least can be streamified, leading to:

return (list1.size()==list2.size() &&         IntStream.range(0, list1.size())                  .allMatch(i -> Arrays.equals(list1.get(i), list2.get(i))); 

Answer 2

1) Solution based on Java 8 streams:

List<List<String>> first = list1.stream().map(Arrays::asList).collect(toList()); List<List<String>> second = list2.stream().map(Arrays::asList).collect(toList()); return first.equals(second); 

2) Much simpler solution (works in Java 5+):

return Arrays.deepEquals(list1.toArray(), list2.toArray()); 

3) Regarding your new requirement (to check the contained String arrays length first), you could write a generic helper method that does equality check for transformed lists:

<T, U> boolean equal(List<T> list1, List<T> list2, Function<T, U> mapper) {     List<U> first = list1.stream().map(mapper).collect(toList());     List<U> second = list2.stream().map(mapper).collect(toList());     return first.equals(second); } 

Then the solution could be:

return equal(list1, list2, s -> s.length)     && equal(list1, list2, Arrays::asList);