Remove duplicates from ArrayList<String[]> - java

Question

I want to remove duplicate from an ArrayList.

If I do this, its working:

 List<String> test = new ArrayList<>();
 test.add("a");
 test.add("a"); //Removing
 test.add("b");
 test.add("c");
 test.add("c"); //Removing
 test.add("d");
 test = test.stream().distinct().collect(Collectors.toList());

But if I want to remove duplicate String[] instead of String, its not removing duplicates:

 List<String[]> test = new ArrayList<>();
 test.add(new String[]{"a", "a"});
 test.add(new String[]{"a", "a"}); // Not removing
 test.add(new String[]{"b", "a"});
 test.add(new String[]{"b", "a"}); // Not removing
 test.add(new String[]{"c", "a"});
 test.add(new String[]{"c", "a"}); // Not removing
 test = test.stream().distinct().collect(Collectors.toList());
 ArrayList<String[]> test2 = (ArrayList<String[]>) test;

Any solution to fix this or another way to remove duplicate of an ArrayList<String[]>? Thanks

• Eran: You'll have to work with List<List<String>> instead of List<String[]>, since arrays don't override Object's equals.
• QuebecSquad: Got it working! Thanks you.

Answer 1

As @Eran notes, you can't work with arrays directly, since they don't override Object.equals(). Hence, arrays a and b are only equal if they are the same instance (a == b).

It's straightforward to convert the arrays to Lists, which do override Object.equals:

List<String[]> distinct = test.stream()
 .map(Arrays::asList) // Convert them to lists
 .distinct()
 .map((e) -> e.toArray(new String[0])) // Convert them back to arrays.
 .collect(Collectors.toList());

Ideone demo