Question

这是我项目的开始：

//class variables
private static int numberOfCouples;
//object arrays 
private static Witch[] witch;
private static Wizard[] wizard;
//ranking arrays
private static int[][] witchPartnerRanking;
private static int[][] wizardPartnerRanking;
//proposal array
private static boolean[][] proposal;

//DO NOT ALTER THE MAIN METHOD
public static void main(String[] args) throws FileNotFoundException {
    go( "coven_dance.txt" );

    System.out.println( "Witch array:" );

    for ( int i = 0; i < witch.length; i++ ) {
        System.out.printf( "Witch %d:, name: %-20s, current partner id: %2d, proposals made: %d%n", 
                            witch[ i ].getId(), witch[ i ].getName(), witch[ i ].getParnerWizardId(), witch[ i ].getNumberOfProposals() );

NullPointerException发生在最后一行。即使我有这个：

 private static void go( String fileName ) throws FileNotFoundException { 


//1. READ THE FILE
    Scanner inStream = new Scanner( new File ( fileName ));
     numberOfCouples = inStream.nextInt();
   // System.out.println(howManyCouples);
    //System.out.print(
   inStream.nextLine();

//2. CREATE AND POPULATE THE witch ARRAY
    /*Witch[]*/ witch = new Witch[numberOfCouples*2];
    /*int [][]*/ witchPartnerRanking = new int[numberOfCouples*2][numberOfCouples];
    for (int i = 0; i < numberOfCouples*2; i++) {
      if(inStream.hasNextInt()){

      //4. CREATE AND POPULATE THE witchPartnerRanking ARRAY

        int j = 0;
         while(inStream.hasNextInt() && j<numberOfCouples){

            int prefer = inStream.nextInt();
              //System.out.println(prefer);
            witchPartnerRanking[i][j] = prefer;
         j++;

         }
         String bob = inStream.nextLine();
          //System.out.println(bob);
      }
      else{
        String name = inStream.next();
          //System.out.println(name);
       Witch the = new Witch(i, name);
        witch[i] = the; 

      }
    }

我不确定发生了什么。如果有人可以提供帮助，那就太棒了。

如果您需要，这是我正在阅读的文件：

4  
 NannyOgg 0 2 3 1  
TiffanyAching 3 2 0 1  
MagratGarlick 0 3 2 1  
GrannyWeatherwax 0 3 2 1  
TheLibrarian 2 1 3 0  
PonderStibbons 2 1 3 0  
LordVetinari 1 2 0 3  
DEATH 3 2 1 0

Answer 1

您正在访问witch数组而未进行初始化。

您已声明但未初始化的private static Witch[] witch;

您需要初始化它。一种方法是：

private static Witch[] witch = new Witch[10]; // replace 10 with any array size you want

在Java中，数组被视为常规对象。每当您访问null的对象时，您都会获得NullPointerException。

为什么我的项目中出现NullPointerException？

1 个答案: