Question

If I have following map:

 NavigableMap<Integer,String> nmap = 
        new TreeMap<Integer,String>(); 

    nmap.put(3, "Three"); 
    nmap.put(1, "One"); 
    nmap.put(4, "Four"); 
    nmap.put(5, "Five"); 
    nmap.put(7, "Seven"); 
    nmap.put(10, "Ten"); 


System.out.println(nmap); 
// {1=One, 3=Three, 4=Four, 5=Five, 7=Seven, 10=Ten} 

Is there a mechanism, that can allow me to print this, printing by index value, if index is smaller more than 1 from the following index print -(dash):

One,-,Three,Four,Five,-,Six,Seven,-,-,Ten

How would I write function for this?

I don’t have to print whole map to string I meant for each key/value pair

Answer 1

Here’s a generalized solution, that also does the concatenation. My generics knownledge is a bit dodgy, so don’t be surprised by the odd mistake:

static <V> List<V> NMapToList(NavigableMap<Integer,V> nmap, V emptyEntryValue)
{
    Integer next = null;
    List<V> list = new ArrayList<V>();

    for(NavigableMap.Entry<Integer, V> e : nmap.entrySet())
    {
        Integer current = e.getKey();

        if(next != null)
            for(int i = next; i < current; i++)
                list.add(emptyEntryValue);
        list.add(e.getValue());

        next = current + 1;
    }

    return list;
}

static String listToString(List<?> l, String separator)
{
    StringBuilder sb = new StringBuilder("(");
    String sep = "";
    for (Object object : l)
    {
        sb.append(sep).append(object.toString());
        sep = separator;
    }
    return sb.append(")").toString();
}

String s = listToString(NMapToList(nmap,'-'),',');