found the solution. Sorry for disturbing:)

whilst its certainly possible (google  'instanceof') its not usually a
good design choice to mix the value types within a collection.

Preferably, have two collections, one for the Integers one for the Strings.

If this is not possible, write a simple data holder class which you can
store both Integer and String inside it, and add an instance of this
dataholder into the collection.

class DataHolder {

public Integer intValue;
public String stringValue;
}

....

map.put(key, dataHolder);

Doing this will be a good start along a design path where very quickly
you find that the dataHolder class needs to have some instance methods
too - it becomes a proper class with its own responsibilities.

A contrived example...

renaming DataHolder to 'Address' and the member vars to houseNumber &
streetName, starts to show that those vars mean something.

class Address {

public Integer houseNumber;
public String streetName;
}

Then we might find that Address should be able to save/update its own
values by setting/getting them from a db...

class Address {

 public Integer houseNumber;
 public String streetName;

 public void refresh() {
   houseNumber = db.getHouseNumber();
   streetName = db.getStreetName;
 }

}

HTH

Andrew