Java代码：学生选课信息。系统至少应包括以下信息： 学生信息：学号、姓名、性别、年级、密码 课程信息：课程编号、课程名称、已选人数、可选人数、授课教师。

下面是一份基于 Java 的学生选课信息系统的代码示例：

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

class Student {
    private String id;
    private String name;
    private String gender;
    private int grade;
    private String password;

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

    // getters and setters
}

class Course {
    private String id;
    private String name;
    private int numSelected;
    private int numAvailable;
    private String teacher;

    public Course(String id, String name, int numSelected, int numAvailable, String teacher) {
        this.id = id;
        this.name = name;
        this.numSelected = numSelected;
        this.numAvailable = numAvailable;
        this.teacher = teacher;
    }

    // getters and setters
}

class CourseSelection {
    private Student student;
    private Course course;

    public CourseSelection(Student student, Course course) {
        this.student = student;
        this.course = course;
    }

    // getters and setters
}

class CourseSelectionSystem {
    private List<Student> students;
    private List<Course> courses;
    private List<CourseSelection> selections;

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

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

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

    public void selectCourse(Student student, Course course) {
        if (course.getNumAvailable() > 0) {
            CourseSelection selection = new CourseSelection(student, course);
            selections.add(selection);
            course.setNumSelected(course.getNumSelected() + 1);
            course.setNumAvailable(course.getNumAvailable() - 1);
            System.out.println("选课成功！");
        } else {
            System.out.println("选课失败，该课程已满！");
        }
    }

    // getters and setters
}

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

        // 添加学生
        Student s1 = new Student("001", "张三", "男", 1, "123456");
        Student s2 = new Student("002", "李四", "女", 2, "123456");
        system.addStudent(s1);
        system.addStudent(s2);

        // 添加课程
        Course c1 = new Course("001", "Java程序设计", 0, 2, "张老师");
        Course c2 = new Course("002", "计算机网络", 0, 3, "李老师");
        system.addCourse(c1);
        system.addCourse(c2);

        // 选课
        System.out.print("请输入学号：");
        String id = scanner.nextLine();
        System.out.print("请输入密码：");
        String password = scanner.nextLine();
        Student student = null;
        for (Student s : system.getStudents()) {
            if (s.getId().equals(id) && s.getPassword().equals(password)) {
                student = s;
                break;
            }
        }
        if (student == null) {
            System.out.println("学号或密码错误！");
            return;
        }
        System.out.println("欢迎您，" + student.getName() + "！");
        System.out.println("可选课程列表：");
        for (Course c : system.getCourses()) {
            System.out.println(c.getId() + "\t" + c.getName() + "\t" + c.getTeacher() + "\t"
                    + c.getNumSelected() + "/" + c.getNumAvailable() + "人");
        }
        System.out.print("请输入课程编号：");
        String courseId = scanner.nextLine();
        Course course = null;
        for (Course c : system.getCourses()) {
            if (c.getId().equals(courseId)) {
                course = c;
                break;
            }
        }
        if (course == null) {
            System.out.println("课程不存在！");
            return;
        }
        system.selectCourse(student, course);
    }
}

该代码实现了一个简单的学生选课信息系统。其中，`Student` 类表示学生，包括学号、姓名、性别、年级和密码等信息；`Course` 类表示课程，包括课程编号、课程名称、已选人数、可选人数和授课教师等信息；`CourseSelection` 类表示学生选课信息，包括学生和课程两个属性；`CourseSelectionSystem` 类表示选课系统，包括学生列表、课程列表和选课记录列表等属性，以及添加学生、添加课程和选课等方法。

在 `Main` 类中，首先创建了一个 `CourseSelectionSystem` 对象，然后添加了两个学生和两门课程。接着，通过输入学生的学号和密码，可以登录选课系统，查看可选课程列表，并选择一门课程进行选课。如果该课程已满，则选课失败。