Java菜单界面学生系统

Question

我试图创建一个学生数据库系统，但我正在努力与界面菜单，当我按1选项1什么都没有发生，还有许多其他错误，像它不会打印。我做错了什么?

下面是RegistryInterface的代码:

package student;
import java.util.Scanner;
public class RegistryInterface
{
    private Registry theRegistry = null;
    Scanner input = new Scanner(System.in);
    public RegistryInterface(Registry theRegistry)
    {
    }
    public void doMenu()
    {
        String decission;
        System.out.println("Registry Main Menun*******************n");
        System.out.println("1. Add a Student n2. Delete a Student"
                + "n3. Print Registryn4. Quit");
        System.out.println("Select Option [1, 2, 3, 4] :>");
        decission = input.nextLine();
        while (decission != "4")
        {
            if ("1".equals(decission))
            {
                doAddStudent();
            }
            if ("2".equals(decission))
            {
                doDeleteStudent();
            }

            if ("3".equals(decission))
            {
                doPrintRegistry();
                break;
            }
            if ("4".equals(decission))
            {
                System.out.println(" System Closing Down.........");
                break;
            }
        }
    }
    private void doAddStudent()
    {
        String addMore = null;
        String foreName;
        String surName;
        int iDNumber;
        while ("y".equals(addMore))
        {
            System.out.println("Add New Studentn***********n");
            System.out.println("Enter forename       :>");
            foreName = input.nextLine();
            System.out.println("nEnter surname      :>");
            surName = input.nextLine();
            System.out.println("Enter ID for Student :>");
            iDNumber = input.nextInt();
            theRegistry.addStudent(new Student(surName, foreName, iDNumber));
            System.out.println("Add Another Student(Y/N) :>");
            addMore = input.nextLine();
        }
    }
    private void doDeleteStudent()
    {
        int studID;
        String another = null;
        System.out.println("Add New Studentn***********n");
        while("y".equals(another))
        {
            System.out.println("Enter Student ID To Delete :>");
            studID = input.nextInt();
            theRegistry.deleteStudent(studID);
            System.out.println("nDelete Another? (Y/N)");
            another = input.nextLine();
        }
    }
    private void doPrintRegistry()
    {
        System.out.println("Printing Registryn***********n");
        theRegistry.format();
    }
}

下面是registryApp的代码:

public class RegistryApp
{
    public static void main(String[] args)
    {
        Registry theRegistry = new Registry();
        RegistryInterface aRegInterface = new RegistryInterface(theRegistry);
        aRegInterface.doMenu();
    }
}

和我的注册类:

import java.util.Iterator;
import java.util.LinkedList;
public class Registry
{
    public LinkedList<Student> studentList = new LinkedList<>();
    public Iterator<Student> iter = studentList.iterator();
    public Registry()
    {
    }
    public void addStudent(Student aStudent)
    {
        Iterator<Student> addIterator = studentList.iterator();
        while (addIterator.hasNext())
        {
            Student ob = addIterator.next();
            if (ob.getStudentID() == aStudent.getStudentID())
            {
                System.out.println("This Student ID "+ aStudent.getStudentID()+ " Is Already Used");
                return;
            }
        }
        System.out.println("Student "+ aStudent.getForeName() + " "
                + "" + aStudent.getForeName() +" "
                + "Successfully Added To System.....n");
        studentList.addLast(aStudent);
    }
    public void deleteStudent(int studentID)
    {
        Iterator<Student> deleteIterator = studentList.iterator();
        boolean removed = false;
        while(deleteIterator.hasNext())
        {
            Student ob = deleteIterator.next();
            if(ob.getStudentID() == studentID)
            {
                deleteIterator.remove();
                removed = true;
                System.out.println(ob.getForeName() + " " + ob.getSurName() + " Was Succesffully Removed from System. n");
            }
        }
        if(!removed)
        {
            System.out.println("Student ID not found");
        }
    }
    public String format()
    {
        StringBuilder sB = new StringBuilder();
        Iterator<Student> formatIterator = studentList.iterator();
        while(formatIterator.hasNext())
        {
            Student ob = formatIterator.next();
            sB.append(ob.format());      
        }
        return sB.toString();
    }
    @Override
    public String toString()
    {
        Iterator<Student> toStringIterator = studentList.iterator();
        StringBuilder sB = new StringBuilder();
        while(toStringIterator.hasNext())
        {
            Student ob = toStringIterator.next();
            sB.append(ob.toString()).append("n");
        }
        return sB.toString();
    }

}

Answer 1

在这个循环中…

while (decission != "4")

…您永远不会将新值设置为decission。因此，循环要么无限运行，要么什么都不做。

另外，你从输入中扫描的字符串将始终是一个新创建的字符串，所以它将始终是!= "4"，即使你输入了"4"。