java - Using Java8 Streams to create a list of objects from another two lists

Question

I have the following Java6 and Java8 code:

List<ObjectType1> lst1 = // a list of ObjectType1 objects
List<ObjectType2> lst2 = // a list of ObjectType1 objects, same size of lst1

List<ObjectType3> lst3 = new ArrayLis<ObjectType3>(lst1.size());
for(int i=0; i < lst1.size(); i++){
  lst3.add(new ObjectType3(lst1.get(i).getAVal(), lst2.get(i).getAnotherVal()));
}

Is there any way in Java8 to handle the previous for in a more concise way using Lambda?

Answer 1

A Stream is tied to a given iterable/Collection so you can't really "iterate" two collections in parallel.

One workaround would be to create a stream of indexes but then it does not necessarily improve over the for loop. The stream version could look like:

List<ObjectType3> lst3 = IntStream.range(0, lst1.size())
         .mapToObj(i -> new ObjectType3(lst1.get(i).getAVal(), lst2.get(i).getAnotherVal()))
         .collect(toList());