How to add element into ArrayList in HashMap

Question

How to add element into ArrayList in HashMap?

    HashMap> Items = new HashMap>();
         


        

Answer 1

HashMap> items = new HashMap>();

public synchronized void addToList(String mapKey, Item myItem) {
    List itemsList = items.get(mapKey);

    // if list does not exist create it
    if(itemsList == null) {
         itemsList = new ArrayList();
         itemsList.add(myItem);
         items.put(mapKey, itemsList);
    } else {
        // add if item is not already in list
        if(!itemsList.contains(myItem)) itemsList.add(myItem);
    }
}