I want to sort a list, using a map which contains the values for each item.
Map<Integer, Float> map = new HashMap<>();
List<Integer> list = new ArrayList<>();
map.put(0, 0.0f);
map.put(1, 5.0f);
map.put(2, 2.0f);
list = new ArrayList<>(map.keySet());
Collections.sort(list, new Comparator<Integer>() {
public int compare(Integer left, Integer right) {
Float leftCost = map.get(left);
Float rightCost = map.get(right);
return leftCost.compareTo(rightCost);
}
})
I want the order to be 0,2,1
because the value of 1
is higher than 2
. But java dont let me do this. I get the following error: Cannot refer to a non-final variable map inside an inner class defined in a different method
How can I do this a way like that?
Just make it final:
final Map<Integer, Float> map = new HashMap<Integer, Float>();
List<Integer> list = new ArrayList<Integer>(); // this assignment is unncessary [1]
map.put(0, 0.0f);
map.put(1, 5.0f);
map.put(2, 2.0f);
list = new ArrayList<Integer>(map.keySet()); // 1. assignment is replaced here
Collections.sort(list, new Comparator<Integer>() {
public int compare(Integer left, Integer right) {
Float leftCost = map.get(left);
Float rightCost = map.get(right);
return leftCost.compareTo(rightCost);
}
})
As your map is mutable, you can still modify it.