직렬화 가능 객체에 대한 입력을 얻으려고 할 때 NullPointerException이 발생했습니다.

Question

3 가지 클래스가 있습니다 : Main, ContactLibrary 및 ContactInfo. ContactLibrary에는 myPhoneBook이라는 ArrayList가 있습니다. ContactInfo는 이름, 주소 등을 포함하는 일련의 문자열로 구성됩니다.

사용자는 예를 들어 이름이나 입력과 관련된 모든 것을 검색하려고합니다. 입력은 ContactLibrary 클래스와 ContactInfo 클래스 (직렬화 가능 객체 모두)에서 수행됩니다.

그러나 그 지점에 도달하면 NPE 오류가 발생합니다.

You have 3 entry(s) saved to disc. 

Hello, and welcome to Team 6's contact list. 
What would you like to do? 
Enter the corresponding number of choice. 

1: Add an entry to the contact list. 
2: Print the entire contact list. 
3: Search for a contact. 
4: Exit the program. 

Please enter a number from 1-4. 
3 
What would you like to search by? 
Exception in thread "main" java.lang.NullPointerException 
    at ContactLibrary.searchByCriteria(ContactLibrary.java:62) 
    at Main.optionsPrompt(Main.java:62) 
    at Main.main(Main.java:25) 
1: Last Names. 
2: Emails. 
3: Zip codes. 

어떻게해야합니까? 여기

은 내 홈페이지 : http://ideone.com/uvfK4U 여기 을 (맨 의견에 다른 두 개의 클래스를 포함합니다)를 UML 다이어그램이다 : http://imgur.com/9W3TS

ContactLibrary 클래스의 요청에 따라 :

/** 
* ContactLibrary, when constructed, creates an ArrayList of ContactLibrary 
* references called myPhoneBook. Every index is made to fill in objects 
* of ContactInfo, which contains entries and credentials. 
* 
* Contains methods to create a new entry, search and print by criteria, and print list. 
*/ 
import java.util.*; 

public class ContactLibrary implements java.io.Serializable { 
    private static final long serialVersionUID = 1L; 
    private ArrayList<ContactInfo> myPhoneBook; 
    private Scanner libraryInput = new Scanner(System.in); 

    /** Constructs the ArrayList that will hold references to ContactInfo. */ 
    public ContactLibrary() { 
     myPhoneBook = new ArrayList<ContactInfo>(); 
    } 

    /** 
    * Adds an entry to the ArrayList and utilizes the set methods in 
    * ContactInfo. 
    */ 
    public void addEntry() { 
     int doAgain = 1; 
     do { 
      myPhoneBook.add(new ContactInfo()); 
      System.out.println("Would you like to enter another contact?"); 
      System.out.println("1: Yes."); 
      System.out.println("2: No."); 
      doAgain = libraryInput.nextInt(); 
     } while (doAgain == 1); 
    } 

    /** 
    * Goes through every index in myPhoneBook and runs ArrayList.get() on them. 
    */ 
    public void printList() { 
     for (int i = 0; i < myPhoneBook.size(); i++) { 
      System.out.println(myPhoneBook.get(i)); 
     } 
    } 

    /** Counts the number of objects within myPhoneBook and returns a string. */ 
    public String scanDisc() { 
     int entryCount = myPhoneBook.size(); 
     return "You have " + entryCount + " entry(s) saved to disc.\n"; 
    } 

    /** 
    * The prompt for having the user search the database via criteria. Asks the 
    * user to enter in their search criteria. 
    */ 
    public void searchByCriteria() { 
     String criteria; 
     //libraryInput = new Scanner("System.in"); 
     int subSubMenuChoice = 0; 
     System.out.println("What would you like to search by?"); 
     System.out.println("1: Last Names."); 
     System.out.println("2: Emails."); 
     System.out.println("3: Zip codes."); 
     subSubMenuChoice = libraryInput.nextInt(); 
     switch (subSubMenuChoice) { 
     case 1: 
      System.out 
        .println("Please enter the last name you'd like to search for:"); 
      criteria = libraryInput.next(); 
      searchByLastName(criteria); 
      break; 
     case 2: 
      System.out 
        .println("Please enter the e-mail you'd like to search for:"); 
      criteria = libraryInput.next(); 
      searchByEmail(criteria); 
      break; 
     case 3: 
      System.out 
        .println("Please enter the zip code you'd like to search for:"); 
      criteria = libraryInput.next(); 
      searchByZip(criteria); 
      break; 
     default: 
      System.out.println("Exiting"); 
      break; 
     } 
    } 

    /** 
    * Loops through every element in the array and returns a toString of that 
    * index for comparing with the search criteria via contains(). 
    */ 
    public void searchByEmail(String criteria) { 
     for (int i = 0; i < myPhoneBook.size(); i++) { 
      if (criteria.compareTo((myPhoneBook.get(i)).getEmail()) == 0) { 
       System.out.println(myPhoneBook.get(i)); 
      } else { 
       System.out.print(""); 
      } 
     } 
    } 

    /** 
    * Loops through every element in the array and returns a toString of that 
    * index for comparing with the search criteria via contains(). 
    */ 
    public void searchByLastName(String criteria) { 
     for (int i = 0; i < myPhoneBook.size(); i++) { 
      if (criteria.compareTo((myPhoneBook.get(i)).getLastName()) == 0) { 
       System.out.println(myPhoneBook.get(i)); 
      } else { 
       System.out.print(""); 
      } 
     } 
    } 

    /** 
    * Loops through every element in the array and returns a toString of that 
    * index for comparing with the search criteria via contains(). 
    */ 
    public void searchByZip(String criteria) { 
     for (int i = 0; i < myPhoneBook.size(); i++) { 
      if (criteria.compareTo((myPhoneBook.get(i)).getZipcode()) == 0) { 
       System.out.println(myPhoneBook.get(i)); 
      } else { 
       System.out.print(""); 
      } 
     } 
    } 

    /** Reorganizes the array in order by last name. */ 
    public void sortData() { 
     Collections.sort(myPhoneBook); 
    } 

} 

Answer 1

당신이 만드는 같은 InputStream에있는 복수의 Scanner 오브젝트. 사용하는 메소드 나 클래스의 constructor의 다음의 클래스에 1 개만 작성해, 그것을 전달하는 것이 최상입니다.

동일한 스트림에서 여러 스캐너 사용. 스캐너는 스트림을 소비 할 수 있으며, 예상되는 부작용을 유발할 수 있습니다. 그것을하지 않는 것이 좋습니다.

당신이 당신의 메인 클래스의 라인 (65)을 대체 할 수있는 다음 nullpointer 그대로 ContactLibrary :

private Scanner libraryInput = new Scanner(System.in);