I’m trying to write a small function that takes two lists and sorts one based on the elements of the other. So something like:
List<Integer> keys = Arrays.asList(3, 5, 2, 4, 1); List<String> valuesToSort = Arrays.asList("A", "B", "C", "D", "E"); List<String> sortedValues = sort(keys, valuesToSort);
would result in a sorted list [E, C, A, D, B]
.
However, valuesToSort
might be a list of something different, like integers, floats or other lists. Ideally, I would want my program to take any list I throw at it, sort it according to keys
, and then return a list of the same type as the input. How would I do that? If the type of values
were fixed, the sorting itself would be straightforward, like for example
public List<String> sort(List<Integer> keys, List<String> values){ Multimap<Integer, String>> multiMap = LinkedListMultimap.create(); for (int i = 0; i < keys.size(); i++) { multiMap.put(keys.get(i), values.get(i)); } List<String>> sortedValues = Lists.newArrayList(); for (Integer key : Ordering.natural().sortedCopy(multiMap.keys())) { for (String value : multiMap.get(key)) { sortedValues.add(value); } } return sortedValues; }
but this only works if values
is a list of the expected type.
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Answer
You can use Generics for this as follow:
public List<T> sort(List<Integer> keys, List<T> values){ Multimap<Integer, T>> multiMap = LinkedListMultimap.create(); for (int i = 0; i < keys.size(); i++) { multiMap.put(keys.get(i), values.get(i)); } List<T> sortedValues = Lists.newArrayList(); for (Integer key : Ordering.natural().sortedCopy(multiMap.keys())) { for (T value : multiMap.get(key)) { sortedValues.add(value); } } return sortedValues; }
Now, when you pass list of strings, the generic T
would be considered as String
. When you pass list of integers, T
would become Integer
. This will happen at runtime.