Java 문법 통합

import java.util.*;
import java.util.stream.*;

// 학생 클래스
record Student(String name, int score) {} // Java 16+ record

public class GradeSystem {
    private List<Student> students = new ArrayList<>();

    public void add(String name, int score) {
        if (score < 0 || score > 100)
            throw new IllegalArgumentException("점수 범위: 0-100");
        students.add(new Student(name, score));
    }

    public double average() {
        return students.stream()
            .mapToInt(Student::score)
            .average()
            .orElseThrow(() -> new RuntimeException("학생 없음"));
    }

    public Map<String, List<Student>> groupByGrade() {
        return students.stream()
            .collect(Collectors.groupingBy(s ->
                s.score() >= 90 ? "A" :
                s.score() >= 80 ? "B" :
                s.score() >= 70 ? "C" : "F"));
    }

    public Student topStudent() {
        return students.stream()
            .max(Comparator.comparingInt(Student::score))
            .orElseThrow();
    }
}

// 실행
GradeSystem gs = new GradeSystem();
gs.add("김철수", 95); gs.add("이영희", 82);
gs.add("박민준", 73); gs.add("최수진", 68);
System.out.printf("평균: %.1f%n", gs.average());
System.out.println("최고: " + gs.topStudent().name());