How to use Collectors.toList for ArrayList?

Question

I am trying to filter my array list by creating a separate variable that stores the top 3 values. However, getting error in collections. I am new to this so any help would be great!

public static ArrayList<exercise> exerciseDetail() {
            ArrayList<exercise> elist = new ArrayList<>();
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Leg Raises", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bridges", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Burpees", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Side Twists", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Planks", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            elist.add(new exercise("Bicycle Crunches", R.drawable.ic_launcher_background, "MEDIUM", "20 Reps or 1 Minute", "Beginner", "Bicycle crunches are a great way to target the rectus abdominis and the obliques in one easy exercise"));
            return elist;



            ArrayList<exercise> filteredExercises = elist.stream().filter(item-> item.getName().equals("Bicycle Crunches") || item.getName().equals("Leg Raises")|| item.getName().equals("Bridges")).collect(Collectors.toList());
        }
    }

Please don't tag questions with the android-studio tag just because you use it: the Android Studio tag should **only** be used when you have questions about the IDE itself, and not any code you write (or want to write) in it. See [when is it appropriate to remove an IDE tag](https://meta.stackoverflow.com/a/315196/6296561), [How do I avoid misusing tags?](https://meta.stackoverflow.com/q/354427/6296561), and [the tagging guide](/help/tagging). Use [android] or other relevant tags instead. — Zoe, Mar 27 '20 at 12:04

score 5 · Answer 1 · answered Mar 27 '20 at 08:55

Collectors.toList() will collect to a List of an intentionally unspecified type. As its documentation says:

There are no guarantees on the type, mutability, serializability, or thread-safety of the List returned…

If you don’t need a specific List with guaranties regarding one of the mentioned traits, just change the declaration of you result variable to

List<exercise> filteredExercises = …

Otherwise, if you really need an ArrayList, use Collectors.toCollection(ArrayList::new) instead of Collectors.toList().

See also this exhaustive list of alternatives.

As a side note, you should try to adhere to the standard naming conventions and use an uppercase letter for the start of your class names.

How to use Collectors.toList for ArrayList?

1 Answers1