Question

I haven’t done Java in a while and i need some suggestions and idea’s regarding data structures.

Currently i am using a TreeMap to map String values to Integer value. I now need to do some calculations and divide the Integer value of the map entry by the the size of the whole map and store this for each entry. I was thinking about using a Map,Integer> but is there a 3 way generics data structure in Java?

My current solution for this is this ..

            int treeSize = occurrence.size();
            String [][] weight = new String[treeSize][2];
            int counter=0;
            double score =0;
            for(Entry<String, Integer> entry : occurrence.entrySet()) {
                weight[counter][0]=entry.getKey();
                score=entry.getValue()/treeSize;
                weight[counter][1]= Double.toString(score);
                counter++;
              }

Answer 1

I would use another object to hold this data:

public Data {
    private int value;
    private double score;

    ...
}

And then type the map as Map<String, Data>. After inserting all the values, you can iterate over the values and update the ratio property for each value in the map. For example:

double size = myMap.size();
for(Map.Entry<String, Data> entry : myMap.entrySet()) {
    Data data = entry.getValue();
    data.setScore(data.getValue() / size); 
}

EDIT

Another thought just came to mind. Instead of calculating the values after you have inserted it, you should probably calculate it as you are inserting it; it’s more efficient that way. Of course, you can only do this if you know the total number of values beforehand.

An even better way is to perform the calculation only when you retrieve a value from the map. There are two advantages to this:

• You don’t need a separate object. Just abstract the access of the value from the map inside another function which returns the value associated with the key, divided by the size of the map.
• Since you don’t have a separate object to maintain the calculated value, you don’t need to update it every time you add or delete a new value.