学生成绩管理系统JAVA

学生成绩管理系统是一个用于录入、查询和输出学生成绩的系统。根据提供的引用内容，该系统具有四个功能：录入学生成绩、查询学生成绩、输出学生按成绩的排名和输出学科的分数。其中，后两个功能在"输出成绩"模块下。

以下是一个使用Java编写的学生成绩管理系统的简单示例：

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class StudentGradeManagementSystem {
    private Map<String, Map<String, Integer>> gradeDatabase;

    public StudentGradeManagementSystem() {
        gradeDatabase = new HashMap<>();
    }

    public void addGrade(String studentName, String subject, int grade) {
        if (!gradeDatabase.containsKey(studentName)) {
            gradeDatabase.put(studentName, new HashMap<>());
        }
        gradeDatabase.get(studentName).put(subject, grade);
    }

    public void queryGrade(String studentName) {
        if (gradeDatabase.containsKey(studentName)) {
            System.out.println("Student: " + studentName);
            System.out.println("Grades:");
            Map<String, Integer> grades = gradeDatabase.get(studentName);
            for (Map.Entry<String, Integer> entry : grades.entrySet()) {
                System.out.println(entry.getKey() + ": " + entry.getValue());
            }
        } else {
            System.out.println("Student not found.");
        }
    }

    public void outputRanking() {
        System.out.println("Ranking:");
        gradeDatabase.entrySet().stream()
                .sorted((e1, e2) -> getTotalGrade(e2.getValue()) - getTotalGrade(e1.getValue()))
                .forEach(entry -> System.out.println(entry.getKey() + ": " + getTotalGrade(entry.getValue())));
    }

    public void outputSubjectGrades(String subject) {
        System.out.println("Subject: " + subject);
        gradeDatabase.entrySet().stream()
                .filter(entry -> entry.getValue().containsKey(subject))
                .forEach(entry -> System.out.println(entry.getKey() + ": " + entry.getValue().get(subject)));
    }

    private int getTotalGrade(Map<String, Integer> grades) {
        int totalGrade = 0;
        for (int grade : grades.values()) {
            totalGrade += grade;
        }
        return totalGrade;
    }

    public static void main(String[] args) {
        StudentGradeManagementSystem system = new StudentGradeManagementSystem();
        Scanner scanner = new Scanner(System.in);

        while (true) {
            System.out.println("Please select an operation:");
            System.out.println("1. Add grade");
            System.out.println("2. Query grade");
            System.out.println("3. Output ranking");
            System.out.println("4. Output subject grades");
            System.out.println("0. Exit");

            int operation = scanner.nextInt();
            scanner.nextLine(); // Consume the newline character

            switch (operation) {
                case 1:
                    System.out.println("Enter student name:");
                    String studentName = scanner.nextLine();
                    System.out.println("Enter subject:");
                    String subject = scanner.nextLine();
                    System.out.println("Enter grade:");
                    int grade = scanner.nextInt();
                    scanner.nextLine(); // Consume the newline character
                    system.addGrade(studentName, subject, grade);
                    break;
                case 2:
                    System.out.println("Enter student name:");
                    studentName = scanner.nextLine();
                    system.queryGrade(studentName);
                    break;
                case 3:
                    system.outputRanking();
                    break;
                case 4:
                    System.out.println("Enter subject:");
                    subject = scanner.nextLine();
                    system.outputSubjectGrades(subject);
                    break;
                case 0:
                    System.exit(0);
                    break;
                default:
                    System.out.println("Invalid operation.");
                    break;
            }
        }
    }
}

这个示例中，我们使用了一个`Map`来存储学生的成绩信息，其中学生姓名作为键，对应的成绩信息作为值。系统提供了添加成绩、查询成绩、输出排名和输出学科成绩的功能。用户可以根据提示选择相应的操作，并根据需要输入相关信息。