用Java写一个学生管理系统，功能要求增加学生信息，查找学生信息，更新学生信息，删除学生信息，退出系统，还要在输入学生信息后返回学生对象，（注：学生信息用数组存储，并且使用单例模式）

以下是一个简单的示例代码，实现了上述功能：

import java.util.Scanner;

public class StudentManagementSystem {
    private static StudentManagementSystem instance = null;  // 单例模式的实例
    private Student[] students;  // 学生信息数组
    private int count;  // 学生信息数量

    private StudentManagementSystem() {
        students = new Student[100];  // 初始化学生信息数组
        count = 0;
    }

    public static StudentManagementSystem getInstance() {
        if (instance == null) {
            instance = new StudentManagementSystem();
        }
        return instance;
    }

    // 增加学生信息
    public void addStudent() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入学生信息：");
        System.out.print("姓名：");
        String name = scanner.nextLine();
        System.out.print("年龄：");
        int age = scanner.nextInt();
        System.out.print("性别：");
        String gender = scanner.next();
        System.out.print("学号：");
        int id = scanner.nextInt();
        Student student = new Student(name, age, gender, id);
        students[count++] = student;
        System.out.println("添加成功！");
    }

    // 查找学生信息
    public void searchStudent() {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入要查找的学生姓名：");
        String name = scanner.nextLine();
        for (int i = 0; i < count; i++) {
            if (students[i].getName().equals(name)) {
                System.out.println(students[i]);
                return;
            }
        }
        System.out.println("没有找到该学生！");
    }

    // 更新学生信息
    public void updateStudent() {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入要更新的学生姓名：");
        String name = scanner.nextLine();
        for (int i = 0; i < count; i++) {
            if (students[i].getName().equals(name)) {
                System.out.println("请输入更新后的学生信息：");
                System.out.print("姓名：");
                name = scanner.nextLine();
                System.out.print("年龄：");
                int age = scanner.nextInt();
                System.out.print("性别：");
                String gender = scanner.next();
                System.out.print("学号：");
                int id = scanner.nextInt();
                students[i].setName(name);
                students[i].setAge(age);
                students[i].setGender(gender);
                students[i].setId(id);
                System.out.println("更新成功！");
                return;
            }
        }
        System.out.println("没有找到该学生！");
    }

    // 删除学生信息
    public void deleteStudent() {
        Scanner scanner = new Scanner(System.in);
        System.out.print("请输入要删除的学生姓名：");
        String name = scanner.nextLine();
        for (int i = 0; i < count; i++) {
            if (students[i].getName().equals(name)) {
                for (int j = i; j < count - 1; j++) {
                    students[j] = students[j+1];
                }
                count--;
                System.out.println("删除成功！");
                return;
            }
        }
        System.out.println("没有找到该学生！");
    }

    // 退出系统
    public void exitSystem() {
        System.out.println("感谢使用学生管理系统，再见！");
        System.exit(0);
    }

    // 主菜单
    public void menu() {
        Scanner scanner = new Scanner(System.in);
        while (true) {
            System.out.println("欢迎使用学生管理系统，请选择要进行的操作：");
            System.out.println("1. 增加学生信息");
            System.out.println("2. 查找学生信息");
            System.out.println("3. 更新学生信息");
            System.out.println("4. 删除学生信息");
            System.out.println("5. 退出系统");
            int choice = scanner.nextInt();
            switch (choice) {
                case 1:
                    addStudent();
                    break;
                case 2:
                    searchStudent();
                    break;
                case 3:
                    updateStudent();
                    break;
                case 4:
                    deleteStudent();
                    break;
                case 5:
                    exitSystem();
                    break;
                default:
                    System.out.println("无效的选择，请重新输入！");
            }
        }
    }

    public static void main(String[] args) {
        StudentManagementSystem system = StudentManagementSystem.getInstance();
        system.menu();
    }
}

class Student {
    private String name;
    private int age;
    private String gender;
    private int id;

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getGender() {
        return gender;
    }

    public void setGender(String gender) {
        this.gender = gender;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    @Override
    public String toString() {
        return "学生信息：" +
                "姓名='" + name + '\'' +
                ", 年龄=" + age +
                ", 性别='" + gender + '\'' +
                ", 学号=" + id;
    }
}