java中的Map上的NullPointerException.怎么了？

Question

我正在尝试使用以下方法将文件加载到Map中:

private static Map<String,Integer> indexVocabulary;
public static Map<String,Integer> getVocabularyFromFile() throws IOException
{
    FileInputStream fstream = new FileInputStream(VOCABULARY_FILE);
    DataInputStream in = new DataInputStream(fstream);
    BufferedReader br = new BufferedReader(new InputStreamReader(in));      
    String line;
    while( (line = br.readLine()) != null )
    {
        LOG.debug(line);
        String[] kv = line.split(" ");
        LOG.debug(kv[0]);
        LOG.debug(Integer.toString(Integer.parseInt(kv[1])));


        indexVocabulary.put(kv[0], Integer.parseInt(kv[1]));
    }
    return indexVocabulary;
}

我可以看到输出line"也kv[0],kv[1]和Integer.parseInt(kv[1])不过我上线一个NullPointerException indexVocabulary.put(kv[0], Integer.parseInt(kv[1]));有谁知道什么是错用这种方法？

Answer 1

你没有初始化indexVocabulary,所以它是null.

更改

private static Map<String,Integer> indexVocabulary;

至

private static Map<String,Integer> indexVocabulary = new HashMap<String,Integer>();