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 \"bett

Answer 1

You could stream over one list and compare to each element of the other by using an iterator:

Iterator it = list1.iterator();
boolean match = list1.size() == list2.size() &&
                list2.stream().allMatch(a -> Arrays.equals(a, it.next()));

Using an iterator instead of the get(index) method on the first list is better because it doesn't matter whether the list is RandomAccess or not.

Note: this only works with a sequential stream. Using a parallel stream will lead to wrong results.

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EDIT: As per the question last edit, which indicates it would be better to check the length of every pair of arrays in advance, I think it could be achieved with a slight modification to my previous code:

Iterator itLength = list1.iterator();
Iterator itContents = list1.iterator();

boolean match = 
        list1.size() == list2.size()
    && 
        list2.stream()
            .allMatch(a -> {
                String[] s = itLength.next();
                return s == null ? a == null :
                       a == null ? s == null :
                       a.length == s.length;
            })
    && 
        list2.stream()
            .allMatch(a -> Arrays.equals(a, itContents.next()));

Here I'm using two iterators and am streaming list2 twice, but I see no other way to check all lengths before checking the contents of the first pair of arrays. Check for lengths is null-safe, while check for contents is delegated to the Arrays.equals(array1, array2) method.