lucene - Calculate DF using Lucene doesn't work

Question

I have an index with 2 docs at the moment (will add some more after everything will work ok). I try to calculate the df for a specific term but I get all the time the total number of docs in the index as a result.for debug purpose I entered a unique string in one doc so the result of the df should be 1. but, it returns 2. at the end of the process I'll need a tf/idf score for every word in the index.

I've tried the following code:

public void calcDF (String term) throws IOException
{

     //open the index file
    Directory dir = FSDirectory.open(new File("d:/index"));
    //create a reader
    IndexReader ir = IndexReader.open(dir);
    //for debug
    System.out.println("num of docs in index : " + ir.maxDoc()); 
    Term t = new Term("content",term);
    int df = ir.docFreq(t);
} 

Tried also with IndexSearcher searcher = new IndexSearcher(ir); instead of indexReader but no luck.

P.S: I'm using lucene 3.5