我正在做一个学校项目，基本上允许用户创建学生，班级，编辑他们，等等。我试图分配id给每个学生，用户创建，现在我允许用户输入自己的id和程序会比较它与其他id，如果id还没有被选择，完成，但如果它已经被选中，将显示一条消息，说它已经被选中，请选择一个不同的id，但我卡在这一部分，这里是我的代码，为简化起见，我只显示了主要和创建学生方法，我会对我的想法发表评论，希望你们能帮我一些想法，请看createstudent（）方法。

import java.util.Scanner;
import java.io.*;
public class MidTermProject {

    public static void main(String[] args) throws IOException {

        Scanner keyboard = new Scanner(System.in);

        System.out.println("Here is the sample of menu choices for Main Menu.");

        System.out.println("\nWelcome to University Enrollment" + "\n1. Create Student" +
                            "\n2. Create Course" + "\n3. Create Enrollment" + "\n4. Edit Student" + "\n5. Edit Course"
                            + "\n6. Edit Enrollment" + "\n7. Display Student" + "\n8. Display Course" + "\n9. Display Enrollment"
                            + "\n10. Grades Sub Menu" + "\n0. --- Quit ---");

        System.out.println("Please enter a valid choice(1-10, 0 to Quit) :");
        int userInput = keyboard.nextInt();

        if(userInput == 1) {
            CreateStudent();
        } else if(userInput == 2) {
            CreateCourse();
        } else if(userInput == 3) {
            CreateEnrollment();
        } else if(userInput == 4 ) {
            EditStudent();
        } else if(userInput == 5) {
            EditCourse();
        } else if(userInput == 6) {
            EditEnrollment();
        } else if(userInput == 7) {
            DisplayStudent();
        } else if(userInput == 8) {
            DisplayCourse();
        } else if(userInput == 9) {
            DisplayEnrollment();
        } else if(userInput == 10) {
            GradesSubMenu();
        } else if(userInput == 0) {
            System.out.print("Done");
        } else {
            System.out.println("Invalid Option, Please try again.");
            userInput = keyboard.nextInt();
            if(userInput == 1) {
                CreateStudent();
            } else if(userInput == 2) {
                CreateCourse();
            } else if(userInput == 3) {
                CreateEnrollment();
            } else if(userInput == 4 ) {
                EditStudent();
            } else if(userInput == 5) {
                EditCourse();
            } else if(userInput == 6) {
                EditEnrollment();
            } else if(userInput == 7) {
                DisplayStudent();
            } else if(userInput == 8) {
                DisplayCourse();
            } else if(userInput == 9) {
                DisplayEnrollment();
            } else if(userInput == 10) {
                GradesSubMenu();
            } else if(userInput == 0) {
                System.out.print("Done");
            }
        }

    }

    public static void CreateStudent() throws IOException {
        String FullName;
        String address;
        String city;
        String state;
        int newStudentID;
        boolean endOfFile = false;

        //Create a Scanner Object
        Scanner keyboard = new Scanner(System.in);

        //Open the file for write
        FileOutputStream fstream =
                new FileOutputStream("StudentInfo.dat");
        DataOutputStream outputFile =
                new DataOutputStream(fstream);

        System.out.print("\nPlease enter your information bellow.\n" + "\nFull Name: ");
        FullName = keyboard.nextLine();
        outputFile.writeUTF(FullName);

        System.out.print("Address: ");
        address = keyboard.nextLine();
        outputFile.writeUTF(address);

        System.out.print("City: ");
        city = keyboard.nextLine();
        outputFile.writeUTF(city);

        System.out.print("State: ");
        state = keyboard.nextLine();
        outputFile.writeUTF(state);

        //Asks the user to enter their own ID
        System.out.print("Please get a Student ID(1-10): ");
        newStudentID = keyboard.nextInt();
        outputFile.writeInt(newStudentID);

        //Once all data is completed, close the file.
        outputFile.close();

        //Open the file for reading.
        FileInputStream team = new FileInputStream("StudentInfo.dat");
        DataInputStream inputFile = new DataInputStream(team);

        //My idea here was to create a for loop to iterate through the file
//to find the already selected IDs, if any of the IDs matches the ID selected by the user 
//then a message will be display to select a different ID, if no match, then done will be displayed.

        System.out.print("\ndone");

        inputFile.close();

    }