映射java int流

Question

I'm learning about streams and I'm trying to map a test score to a letter grade using a stream. I think I'm close but I can't figure out the code to map it. The part that I'm hung up on is the Map at the end of the code. Here's the code that I have.

import java.util.ArrayList;
import java.util.Arrays;
import static java.util.Collections.list;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;
import java.util.function.Function;
import java.util.stream.Collectors;

public class LetterGrades {

public static void main(String[] args) {
    List<String> gradeMap = new ArrayList<>();
    GradeBook[] grades = {
        new GradeBook(90, "A"),
        new GradeBook(80, "B"),
        new GradeBook(70, "C"),
        new GradeBook(60, "D"),
        new GradeBook(0, "F")};
    List<GradeBook> list = Arrays.asList(grades);
//        gradeMap.add("A");
//        gradeMap.add("B");
//        gradeMap.add("C");
//        gradeMap.add("D");
//        gradeMap.add("F");
    //List<Integer> grades = new ArrayList<Integer>();

//        grades.add(94);
//        grades.add(85);
//        grades.add(91);
//        grades.add(100);
//        grades.stream()

//               .forEach(System.out::println);
    Map<String, Integer> grade = list.stream().
            collect(Collectors.groupingBy(GradeBook::getLetterGrade,
                    Collectors.joining(GradeBook::getScore)));
    System.out.println(grade);

}
}

Answer 1

You can simply use Collectors.toMap() :

Map<String, Integer> grade = list.stream().collect(
    Collectors.toMap(GradeBook::getLetterGrade, GradeBook::getScore)
);