Hashtable overwriting issue in java

Question

I am studying java and I am having trouble using put to add data into a Java hashtable.

I have this code

double finalIDF = 0.0;
double finalIDF = 0.0;
double finalBM = 0.0;

ArrayList<Double> finalTMlist = new ArrayList<Double>();
 Hashtable<String, ArrayList<Double>> BM25TFIDF = new Hashtable<String, ArrayList<Double>>();
 String[] bm25QueryList // this is the array to store strings like {hey , good , by}

 for(int finalindex = 0; finalindex < bm25QueryList.length ; finalindex++)
{
actualTFvalueforEachDoc.clear();
finalTMlist.clear();
finalIDF = 0.0;
finalIDF = htBM25IDF.get(bm25QueryList[finalindex]);
finalTMlist = tfForAlldoc.get(bm25QueryList[finalindex]);


 for(int innerfinal = 0 ; innerfinal < finalTMlist.size() ; innerfinal++ ){
 finalTM =finalTMlist.get(innerfinal);
finalBM =  finalIDF * finalTM;
actualTFvalueforEachDoc.add(finalBM); 
finalTM = 0.0;
finalBM = 0.0;   }
 BM25TFIDF.put(bm25QueryList[finalindex], actualTFvalueforEachDoc);
 System.out.println("Right before final step after BM25TFIDF " + BM25TFIDF);  }

I would like to put the ArrayList<Double> into the hashtable using a String key.

The first time through the loop I got the key "orange"

 Right before final step after BM25TFIDF {orange=[1.1698113207547172, 1.0508474576271187, 0.8682367918523235, 1.6330439988027539, 0.8938401048492793, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 1.0133729569093612, 0.0]} 

which is fine

However, when I insert the second arraylist with second string key "bye" I get

Right before final step after BM25TFIDF {orange=[0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 4.238037326690413, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0], bye=[0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 4.238037326690413, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]}

It is overwriting the first arraylist. I used string array to change the key every time, so it shouldn't be happen.

I am not really sure the reason that it keeps over writing.

does anyone know the reason ?

Answer 1

Don't do finalTmList.clear() in your for loop. That will clear the list pointed to by the finalTmList , and subsequently for all the reference pointing to that list.

Since, when you add a list to the Map , you are not adding a copy of your List , rather a copy of your List Reference , that points to the same List . So, any change you make to that list with that reference, or any reference pointing to the list, will be reflected in all the reference.

You should rather create a new list in your for loop, for each entry of your Map: -

finalTMlist = new ArrayList<Double>();

Move the above statement inside your first for loop.

for(int finalindex = 0; finalindex < bm25QueryList.length ; finalindex++) {
    finalTMlist = new ArrayList<Double>();
    // Your rest code.

And follow the same thing for actualTFvalueforEachDoc.clear() also, whatever it is, as I can't see the declaration in the code.

Answer 2

您应该为地图中的每个条目创建一个新的ArrayList 。

Answer 3

您必须先创建新的数组列表，然后再开始新的迭代

actualTFvalueforEachDoc = new ArraList<Double>();