英文:
How to improve this code snippet in imperative way?
问题
以下是翻译好的部分：
以下代码片段具有访问全局变量的副作用，我该如何改进这个代码片段？
double total = 0;
for (Student s : myStudentList){
total = total + s.getSchScore();
}
System.out.println(total + " is total marks.");
英文:
The code snippet below has accessing global variable side affect, how can I improve this code snippet?
double total = 0;
for (Student s : myStudentList){
total = total + s.getSchScore();
}
System.out.println(total + " is total marks.");
答案1
得分: 2
Sure, here's the translated code portion:
如果你愿意/能够输入列表 (ArrayList<Student> myStudentList = new ArrayList<>();)，可能的解决方案是
final double total = myStudentList.stream()
.mapToDouble(Student::getScore)
.sum();
如果你必须/想要继续使用原始类型列表（这是强烈不推荐的），那么我建议两个额外的步骤：过滤掉所有非Student对象并将对象强制转换为Student：
final double total = ((List<?>) myStudentList).stream()
.filter(o -> o instanceof Student)
.map(o -> (Student) o)
.mapToDouble(Student::getScore)
.sum();
英文:
If you are willing/able to type the list (ArrayList<Student> myStudentList = new ArrayList<>();) a possible solution woudl be
final double total = myStudentList.stream()
.mapToDouble(Studen::getScore)
.sum();
If you must/want to continue with the raw type list (which is highly discouraged), then I would recommend two additional steps: filter out all non-Student-objects and cast the objects to Student:
final double total = ((List<?>) myStudentList).stream()
.filter(o -> o instanceof Student)
.map(o -> (Student) o)
.mapToDouble(Studen::getScore)
.sum();
答案2
得分: 0
使用原始类型是强烈不推荐的，因为它需要将每个对象转换为所需的类型。
如果List声明为具有Student作为类型参数，代码将得到很大的改善。
英文:
Using raw types is strongly discouraged, as it requires casting each Object to the required type.
final double total = myStudentList.stream().mapToDouble(x -> ((Student) x).getStudentMark()).sum();
If the List was declared with Student as the type parameter, the code would be much improved.
List<Student> myStudentList = new ArrayList<>();
//...
final double total = myStudentList.stream().mapToDouble(Student::getStudentMark).sum();
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