자바 메뉴 인터페이스 학생 시스템

Question

좋아, 메신저 학생 데이터베이스 시스템을 괴롭 히고 있지만 인터페이스 메뉴로 고생하고있다. 옵션 1을 위해 1을 누르면 아무 일도 일어나지 않고 인쇄와 같은 많은 다른 오류가 발생한다. 내가 도대체 ​​뭘 잘못하고있는 겁니까?

는 RegistryInterface에 대한 Heres는 코드 :

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 Menu\n*******************\n"); 
     System.out.println("1. Add a Student \n2. Delete a Student" 
       + "\n3. Print Registry\n4. 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 Student\n***********\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 Student\n***********\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 Registry\n***********\n"); 
     theRegistry.format(); 
    } 
} 

그리고 heres는 코드 registryApp에 대한 :

public class RegistryApp 
{ 

    public static void main(String[] args) 
    { 
     Registry theRegistry = new Registry(); 

     RegistryInterface aRegInterface = new RegistryInterface(theRegistry); 

     aRegInterface.doMenu(); 

    } 
} 

그리고 내 레지스터 클래스 :

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

이 루프 내부 ...

while (decission != "4") 

... 새 값을 decission으로 설정하지 않았습니다. 따라서 루프는 무한히 실행되거나 아무 것도 수행하지 않습니다.

또한 입력에서 스캔 한 문자열은 항상 새로 생성 된 문자열이므로 "4"를 입력해도 항상! = "4"가됩니다.