Question

I have an object as Riziv with three variables as id, cnk and product. Then I search in a databank for this object and add it to a ArrayList as ArrayList<Riziv> list.
Now I should checkout if all object in his array are the same cnk then return true otherwise I should return all objects which are not the same cnk with error message.

  public class Riziv{ String id, cnk, product; }
    ArrayList<Riziv> list = getArrayListFromDatabank(id);

    public void getDuplicatedWhichHasTheSameCnk(){

    }
  }

Answer 1

Using standard JVM structures (MultiMap is provided by guava), you can do that:

public List<Riviz> getDuplicates(final List<Riviz> l)
{
    final HashMap<String, List<Riviz>> m = new HashMap<String, List<Riviz>>();
    final List<Riviz> ret = new ArrayList<Riviz>();

    String cnk;

    for (final Riviz r: l) {
        cnk = r.getCnk();
        if (!m.contains(cnk))
            m.add(cnk, new ArrayList<Riviz>());
        m.get(cnk).add(r);            
    }

    List<Riviz> tmp;
    for (final Map.Entry<String, List<Riviz>> entry: m.entrySet()) {
        tmp = entry.getValue();
        if (tmp.size() == 1) // no dups
            continue;
        ret.addAll(tmp);
    }

    return ret;
}

ret will contain the duplicates. You can change that function to return a Map<String, Riviz> instead, and filter out entries where the list size is only one. You’ll then get a map with the conflicting cnks as keys and a list of dups as values.