I am trying to use a stream for something and I think I have a conceptual misunderstanding. I am trying to take an array, convert it to a stream, and .forEach item in the array I want to run a function and return a list of the results of that function from the foreach.
Essentially this:
Thing[] functionedThings = Array.stream(things).forEach(thing -> functionWithReturn(thing))
Is this possible? Am I using the wrong stream function?
What you are looking for is called the map operation:
Thing[] functionedThings = Arrays.stream(things).map(thing -> functionWithReturn(thing)).toArray(Thing[]::new);
This method is used to map an object to another object; quoting the Javadoc, which says it better:
Returns a stream consisting of the results of applying the given function to the elements of this stream.
Note that the Stream is converted back to an array using the toArray(generator) method; the generator used is a function (it is actually a method reference here) returning a new Thing array.
You need map not forEach
List<Thing> functionedThings = Array.stream(things).map(thing -> functionWithReturn(thing)).collect(Collectors.toList());
Or toArray() on the stream directly if you want an array, like Holger said in the comments.
Collectors.toArray(). Instead, the Stream itself offers a toArray() method.In my case I had to use some setter of Thing, so used peek(...)
List<Thing> functionedThings = Array.stream(things)
.peek(thing -> thing.setSuccess(true))
.collect(Collectors.toList());
StreamAPI. It has more methods than justforEach.