Java 8 List into Map

Question

I want to translate a List of objects into a Map using Java 8\'s streams and lambdas.

This is how I would write it in Java 7 and below.

private Map&l         


        

Answer 1

I will write how to convert list to map using generics and inversion of control. Just universal method!

Maybe we have list of Integers or list of objects. So the question is the following: what should be key of the map?

create interface

public interface KeyFinder {
    K getKey(E e);
}

now using inversion of control:

  static  Map listToMap(List list, KeyFinder finder) {
        return  list.stream().collect(Collectors.toMap(e -> finder.getKey(e) , e -> e));
    }

For example, if we have objects of book , this class is to choose key for the map

public class BookKeyFinder implements KeyFinder {
    @Override
    public Long getKey(Book e) {
        return e.getPrice()
    }
}