Best way in java to merge two lists to one map?

Question

Possible Duplicate:
Clearest way to combine two lists into a map (Java)?

Given this:

    List<Integer> integers = new ArrayList<Integer>();
    List<String> strings = new ArrayList<String>();

    strings.add("One");
    strings.add("Two");
    strings.add("Three");

    integers.add(new Integer(1));
    integers.add(new Integer(2));
    integers.add(new Integer(3));

What is the best way to merge these lists into a map like ["One" => 1, "Two" => 2, "Three"=>3]?

Thanks for any suggestions

Answer 1

Assuming, that both lists are of equal length and that keys and values have the same index in both lists, then this is an easy approach:

for (int i = 0; i < strings.size(); i++) {
  map.put(strings.get(i), integers.get(i));
}

Answer 2

Something like:

HashMap<String,Integer> hmap=new HashMap<String,Integer>();

for (int i=0; i<strings.size(); i++) {
  hmap.put(strings.get(i),integers.get(i));
}

Answer 3

Over here in Scala land, we'd write it as:

integers.zip(strings).toMap

:-P

Answer 4

Code suggested by Andreas or Mikera is fine as long as the List implementation you are using has an efficient get method. There may be cases where access by index is rather expensive (for example, LinkedList).

That's why, in general, you should prefer iterators for such procedures.

Code:

Iterator<String> stringsItr = strings.iterator();
Iterator<Integer> integersItr = integers.iterator();
Map<String, Integer> map = new HashMap<String, Integer>();
while(stringsItr.hasNext() && integers.hasNext()) {
  map.put(stringsItr.next(), integers.next());
}