Question

I have a Map like this :

Map<String,GridCell> cellsMap

I pass this into a method and the return from that method should contain a Map(say answerMap) which contains all the entries of cellsMap map plus an extra entry that contains a String as the key and a String as the value . Something like :

  Map<String,Object> answerMap  = new ConcurrentHashMap<String,Object>();
    //answer should first contain all the map entries of cellsMap and then add an extra entry like the following
    answer.put(getId(), getSelectionValue()); // getSelectionValue() returns a String that contains coordinates of the selected cells.
     return answerMap; 

Answer 1

Have you considered the Map.putAll() method ?

e.g.

answerMap.putAll(cellsMap);

I don’t think this is a good object model, by the way. I think you’re better off creating a new class that contains your original map (maybe a copy) and an additional field for your String/String pair.

Otherwise you’re throwing objects of different types into the same map, and that’s going to make life complicated when you later extract that info. Each time you extract via a key you’re going to have to check the type of the object returned. Note that ConcurrentHashMaps don’t maintain insertion order.