学生成绩管理系统java，200行代码

好的，下面是一个不到200行的Java实现，包括了学生类、学生管理类和主函数：

1. 学生类

public class Student {
    private String id;
    private String name;
    private int grade;

    public Student(String id, String name, int grade) {
        this.id = id;
        this.name = name;
        this.grade = grade;
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public int getGrade() {
        return grade;
    }

    @Override
    public String toString() {
        return "学号：" + id + "，姓名：" + name + "，成绩：" + grade;
    }
}

2. 学生管理类

import java.util.ArrayList;
import java.util.List;

public class StudentManager {
    private List<Student> students;

    public StudentManager() {
        students = new ArrayList<>();
    }

    public void addStudent(Student student) {
        students.add(student);
    }

    public void removeStudent(Student student) {
        students.remove(student);
    }

    public Student findStudentById(String id) {
        for (Student student : students) {
            if (student.getId().equals(id)) {
                return student;
            }
        }
        return null;
    }

    public List<Student> findStudentByName(String name) {
        List<Student> result = new ArrayList<>();
        for (Student student : students) {
            if (student.getName().equals(name)) {
                result.add(student);
            }
        }
        return result;
    }

    public double getAverageGrade() {
        double sum = 0.0;
        for (Student student : students) {
            sum += student.getGrade();
        }
        return sum / students.size();
    }

    public List<Student> getAllStudents() {
        return students;
    }
}

3. 主函数

import java.util.List;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        StudentManager manager = new StudentManager();

        System.out.println("欢迎使用学生成绩管理系统！");
        while (true) {
            System.out.println("请选择操作：");
            System.out.println("1. 添加学生");
            System.out.println("2. 删除学生");
            System.out.println("3. 根据学号查询学生");
            System.out.println("4. 根据姓名查询学生");
            System.out.println("5. 显示所有学生");
            System.out.println("6. 计算平均分");
            System.out.println("0. 退出");

            int choice = scanner.nextInt();
            switch (choice) {
                case 1:
                    System.out.println("请输入学号、姓名和成绩：");
                    String id = scanner.next();
                    String name = scanner.next();
                    int grade = scanner.nextInt();
                    Student student = new Student(id, name, grade);
                    manager.addStudent(student);
                    System.out.println("添加成功！");
                    break;
                case 2:
                    System.out.println("请输入要删除的学生的学号：");
                    String idToDelete = scanner.next();
                    Student studentToDelete = manager.findStudentById(idToDelete);
                    if (studentToDelete == null) {
                        System.out.println("该学生不存在！");
                    } else {
                        manager.removeStudent(studentToDelete);
                        System.out.println("删除成功！");
                    }
                    break;
                case 3:
                    System.out.println("请输入要查询的学生的学号：");
                    String idToFind = scanner.next();
                    Student studentToFind = manager.findStudentById(idToFind);
                    if (studentToFind == null) {
                        System.out.println("该学生不存在！");
                    } else {
                        System.out.println(studentToFind);
                    }
                    break;
                case 4:
                    System.out.println("请输入要查询的学生的姓名：");
                    String nameToFind = scanner.next();
                    List<Student> students = manager.findStudentByName(nameToFind);
                    if (students.isEmpty()) {
                        System.out.println("该学生不存在！");
                    } else {
                        for (Student s : students) {
                            System.out.println(s);
                        }
                    }
                    break;
                case 5:
                    List<Student> allStudents = manager.getAllStudents();
                    if (allStudents.isEmpty()) {
                        System.out.println("暂无学生信息！");
                    } else {
                        for (Student s : allStudents) {
                            System.out.println(s);
                        }
                    }
                    break;
                case 6:
                    double avgGrade = manager.getAverageGrade();
                    System.out.println("平均分：" + avgGrade);
                    break;
                case 0:
                    System.out.println("感谢使用学生成绩管理系统！");
                    System.exit(0);
                    break;
                default:
                    System.out.println("无效的选择，请重新输入！");
            }
        }
    }
}

以上代码实现了一个简单的学生成绩管理系统，包括添加学生、删除学生、查询学生、统计平均分等功能。注意，该实现仅供参考，您可以根据自己的需求进行修改和完善。