从lucene索引中获取文档的顶级术语频率时出现“无包含实例错误”

我正在尝试获取lucene索引中每个特定文档的最常见术语频率。我正试图设定我所关心的最热门的术语的上限,也许是20

然而,当调用比较器时,我得到的是“displaytermvorts类型的不包含实例是可访问的”…

所以对于这个函数,我传递每个文档的向量和我想知道的最大顶项

protected static Collection getTopTerms(TermFreqVector tfv, int maxTerms){
  String[] terms = tfv.getTerms();   
  int[] tFreqs = tfv.getTermFrequencies();  

  List result = new ArrayList(terms.length); 

  for (int i = 0; i < tFreqs.length; i++) {
    TermFrq tf = new TermFrq(terms[i], tFreqs[i]);
    result.add(tf); 

  }
  Collections.sort(result, new FreqComparator()); 
  if(maxTerms < result.size()){
    result = result.subList(0, maxTerms);
  }
  return result; 
}
/*Class for objects to hold the term/freq pairs*/

static class TermFrq{
   private String term;
   private int freq;

   public TermFrq(String term,int freq){
   this.term = term;
   this.freq = freq;
 }
   public String getTerm(){
   return this.term;
 }
 public int getFreq(){
   return this.freq;
 }
}


/*Comparator to compare the objects by the frequency*/
 class FreqComparator implements Comparator{
  public int compare(Object pair1, Object pair2){
   int f1 = ((TermFrq)pair1).getFreq();
   int f2 = ((TermFrq)pair2).getFreq();

   if(f1 > f2) return 1;
   else if(f1 < f2) return -1;
   else return 0;
  }
}

解释和更正我将非常感谢,而且如果有人有经验的术语频率提取和做得更好的方式,我对所有的建议开放!

请帮助!!!!谢谢!