能用Java写出一个学生选课管理系统吗

当然可以！以下是一个简单的学生选课管理系统的Java代码示例，供你参考：

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

public class CourseSelectionSystem {

    private Map<String, Student> students;
    private Map<String, Course> courses;

    public CourseSelectionSystem() {
        students = new HashMap<>();
        courses = new HashMap<>();
    }

    public void addStudent(Student student) {
        students.put(student.getId(), student);
    }

    public void addCourse(Course course) {
        courses.put(course.getCode(), course);
    }

    public void assignCourse(String studentId, String courseCode) {
        Student student = students.get(studentId);
        Course course = courses.get(courseCode);
        if (student != null && course != null) {
            student.addCourse(course);
            course.addStudent(student);
        }
    }

    public void dropCourse(String studentId, String courseCode) {
        Student student = students.get(studentId);
        Course course = courses.get(courseCode);
        if (student != null && course != null) {
            student.removeCourse(course);
            course.removeStudent(student);
        }
    }

    public void printStudents() {
        for (Student student : students.values()) {
            System.out.println(student);
        }
    }

    public void printCourses() {
        for (Course course : courses.values()) {
            System.out.println(course);
        }
    }

    public static void main(String[] args) {
        CourseSelectionSystem system = new CourseSelectionSystem();

        // Add students
        system.addStudent(new Student("001", "Alice"));
        system.addStudent(new Student("002", "Bob"));
        system.addStudent(new Student("003", "Charlie"));

        // Add courses
        system.addCourse(new Course("CS101", "Introduction to Computer Science"));
        system.addCourse(new Course("MATH101", "Calculus I"));
        system.addCourse(new Course("PHYS101", "Physics I"));

        // Assign courses to students
        system.assignCourse("001", "CS101");
        system.assignCourse("001", "MATH101");
        system.assignCourse("002", "MATH101");
        system.assignCourse("003", "PHYS101");

        // Drop a course
        system.dropCourse("001", "MATH101");

        // Print students and courses
        System.out.println("Students:");
        system.printStudents();
        System.out.println("Courses:");
        system.printCourses();
    }
}

class Student {

    private String id;
    private String name;
    private List<Course> courses;

    public Student(String id, String name) {
        this.id = id;
        this.name = name;
        courses = new ArrayList<>();
    }

    public String getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public void addCourse(Course course) {
        courses.add(course);
    }

    public void removeCourse(Course course) {
        courses.remove(course);
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("Student ID: ").append(id).append("\n");
        sb.append("Name: ").append(name).append("\n");
        sb.append("Courses: ");
        if (courses.isEmpty()) {
            sb.append("None");
        } else {
            for (Course course : courses) {
                sb.append(course.getCode()).append(", ");
            }
            sb.delete(sb.length() - 2, sb.length());
        }
        sb.append("\n");
        return sb.toString();
    }
}

class Course {

    private String code;
    private String name;
    private List<Student> students;

    public Course(String code, String name) {
        this.code = code;
        this.name = name;
        students = new ArrayList<>();
    }

    public String getCode() {
        return code;
    }

    public String getName() {
        return name;
    }

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

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

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("Course Code: ").append(code).append("\n");
        sb.append("Name: ").append(name).append("\n");
        sb.append("Students: ");
        if (students.isEmpty()) {
            sb.append("None");
        } else {
            for (Student student : students) {
                sb.append(student.getName()).append(", ");
            }
            sb.delete(sb.length() - 2, sb.length());
        }
        sb.append("\n");
        return sb.toString();
    }
}

这个简单的学生选课管理系统包含了学生和课程两个类，并且实现了添加学生、添加课程、为学生分配课程、为学生删除课程、输出所有学生信息和输出所有课程信息等功能。你可以根据自己的需要进行修改和扩展。