Question

I use Arraylist and inserting Objects to specific index.(for example is element at index of 0 and 2 but it is not at at index of 1)And I want to know if I should use Arraylist.add(id,obj) or Arraylist.set(id,obj) . I use the following test if(Arraylist.get(t.imgIdx) == null) , but it throws me Exception out of bounds all the time. How can/should I test it?

public static int GiveBackAverageID(Vector<DMatch> lista){

        ArrayList<CMatch> workingList = new ArrayList<CMatch>();

        for (DMatch t : lista){
            if(workingList.get(t.imgIdx) == null){
                workingList.add(t.imgIdx, new CMatch(t.imgIdx,t.distance,1));
            }else{
                CMatch pom = workingList.get(t.imgIdx);
                pom.setSummaDist(pom.getSummaDist()+t.distance);
                pom.setCount(pom.getCount()+1);
                workingList.set(t.imgIdx, pom);
            }
        }
...

thanks
Csabi

Answer 1

If you want to test if an object is at a position, use IndexOf(). This method returns -1 if the object is not in the list.

UPDATE

On your new piece of code:

public static int GiveBackAverageID(Vector<DMatch> lista){

    ArrayList<CMatch> workingList = new ArrayList<CMatch>();

    for (DMatch t : lista){
        if(t.imgIdx >= workingList.size() || t.imgIdx < 0)
        {
            // do something with wrong indices.
        }
        else
        {
            if(workingList.get(t.imgIdx) == null){
                workingList.add(t.imgIdx, new CMatch(t.imgIdx,t.distance,1));
            }else{
                CMatch pom = workingList.get(t.imgIdx);
                pom.setSummaDist(pom.getSummaDist()+t.distance);
                pom.setCount(pom.getCount()+1);
                workingList.set(t.imgIdx, pom);
            }
        }
    }
}

Or what you could also do, is generate more capacity in your workingList:

public static int GiveBackAverageID(Vector<DMatch> lista){

    // Creating more capacity in the constructor!
    ArrayList<CMatch> workingList = new ArrayList<CMatch>(lista.size());

    for (DMatch t : lista){
        if(workingList.get(t.imgIdx) == null){
            workingList.add(t.imgIdx, new CMatch(t.imgIdx,t.distance,1));
        }else{
            CMatch pom = workingList.get(t.imgIdx);
            pom.setSummaDist(pom.getSummaDist()+t.distance);
            pom.setCount(pom.getCount()+1);
            workingList.set(t.imgIdx, pom);
        }
    }
}

As a better alternative, I would use a HashTable<int,DMatch> instead.