android - 如何对ArrayList使用Collectors.toList？

Question

我试图通过创建一个存储前 3 个值的单独变量来过滤数组列表。但是，在集合中出现错误。我对此很陌生，所以任何帮助都会很棒!

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());
        }
    }

Answer 1

Collectors.toList() 将收集到有意未指定类型的 List 中。如its documentation说:

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

如果您不需要特定的 List 来保证上述特征之一，只需将结果变量的声明更改为

List<exercise> filteredExercises = …

否则，如果您确实需要 ArrayList，请使用 Collectors.toCollection(ArrayList::new) 而不是 Collectors.toList() .

另请参阅this exhaustive list of alternatives .

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顺便说一句，您应该尝试遵守标准命名约定，并使用大写字母作为类名的开头。