Inverting a Scrabble letter score map

Question:


The old system stored a list of letters per score:


1 point: "A", "E", "I", "O", "U", "L", "N", "R", "S", "T",


2 points: "D", "G",


3 points: "B", "C", "M", "P",


4 points: "F", "H", "V", "W", "Y",


5 points: "K",


8 points: "J", "X",


10 points: "Q", "Z",


The shiny new scrabble system instead stores the score per letter, which makes it much faster and easier to calculate the score for a word. It also stores the letters in lower-case regardless of the case of the input letters:


"a" is worth 1 point.


"b" is worth 3 points.


"c" is worth 3 points.


"d" is worth 2 points.


Etc.


Your mission, should you choose to accept it, is to write a program that transforms the legacy data format to the shiny new format.

Code:

import java.util.Map;
import java.util.List;
import java.util.HashMap;

import com.google.inject.AbstractModule;

public class Etl extends AbstractModule {
  public Map transform(Map> oldData) {
    Map items = new HashMap();

    for(Map.Entry> entry: oldData.entrySet()) {
      for(String chr: entry.getValue()) {
       items.put(chr.toLowerCase(), entry.getKey()); 
      }
    }
    return items;
  }
}

Can the above code be made more readable and optimized?

The two things I would change:

• The Map you're returning should have type parameters.

• The key is best to be a Character rather than a String.

Other than that, I don't see much more to it than what you've got there already.

StackExchange Code Review Q#143612, answer score: 2