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List故意未指定的类型。正如其文档所述：

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List不保证返回的\xe2\x80\xa6的类型、可变性、可序列化性或线程安全性

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如果您不需要\xe2\x80\x99t 需要List有关上述特征之一的特定保证，只需将结果变量的声明更改为

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List<exercise> filteredExercises = \xe2\x80\xa6\n

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

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另请参阅此详尽的替代方案列表。

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作为旁注，您应该尝试遵守标准命名约定并使用大写字母作为类名称的开头。

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