How to code the set method of a Map with another Map as value?

Question

I normally do this to set a new Map to a private variable:

public static void setListaClausulas(Map<String, Clausula> nvLista) {
    listaClausulas = new TreeMap<String, Clausula>(nvLista);
}

I suppose this is ok to set a new copy of the nvLista and all it's members and not a reference, is it?

But now I have a Map inside another Map and I'm doing this:

public static void setListaClausulas(Map<String, Map<String, Clausula>> nvLista) {
    listaClausulas = new TreeMap<String, Map<String, Clausula>>(nvLista);
}

Is this the correct way to do it or do you recommend something else? What I want is to set a new copy of nvLista (and all it's elements) and not copy just the reference.

Answer 1

I guess you are worried about the maps being passed in your method parameter will be mutated?

You need to create a deep-copy of the parameter. Various approaches are discussed in this SO question, deep-clone-utility-recomendation

EDIT: In response to comment, here's a coded version. This doesn't deep copy the Clausula instances, since they were not copied before - I'm assuming they're immutable.

public Map<String, Map<String, Clausula>> deepCopy(Map<String, Map<String, Clausula>> nvLista)
{
   Map<String, Map<String, Clausula>> target = new TreeMap<String, Map<String, Clausula>>();
   for (String key: nvLista.keySet()) {
       Map<String, Clausula> value = nvLista.get(key);
       target.put(key, new TreeMap<String,Clausula>(value));
   }
   return target;
}

However, nesting collection types like this quickly becomes unreadable. If you can change the code, it may help readability to create a wrapper object for the innermost map.

Answer 2

Deep copying is hard for general case, but you could do this to solve your particular problem:

static Map< String, Map< String, Clausula > > deepCopy (
        final Map< String, Map< String, Clausula > > source
    )
{
    final TreeMap< String, Map< String, Clausula> > result  =
        new TreeMap< String, Map<String,Clausula> >( );

    for (
        final Map.Entry< String, Map< String, Clausula> > cur :
            source.entrySet( )
    )
    {
        result.put(
            cur.getKey( ),
            new TreeMap< String, Clausula >( cur.getValue( ) )
        );
    }

    return result;
}