Convert IntStream to Map

Question

I have an IntStream and want for each element of that stream to do some calculations and return them as Map where keys are int values and values are result of that computations. I wrote following piece of code:

IntStream.range(0,10)
    .collect(
        Collectors.toMap(Function.identity(), i -> computeSmth(i)));

where computeSmth(Integer a). I got next compiler error

method collect in interface java.util.stream.IntStream cannot be applied to given types;
 required: java.util.function.Supplier<R>,java.util.function.ObjIntConsumer<R>,java.util.function.BiConsumer<R,R>
 found: java.util.stream.Collector<java.lang.Object,capture#1 of ?,java.util.Map<java.lang.Object,java.lang.String>>
 reason: cannot infer type-variable(s) R
   (actual and formal argument lists differ in length)

What I'm doing wrong?

Solution

Here is my code, it will work for you.

Function Reference version

public class AppLauncher {

public static void main(String a[]){
    Map<Integer,Integer> map = IntStream.range(1,10).boxed().collect(Collectors.toMap(Function.identity(),AppLauncher::computeSmth));
    System.out.println(map);
}
  public static Integer computeSmth(Integer i){
    return i*i;
  }
}

Lambda expression version

public class AppLauncher {

    public static void main(String a[]){
        Map<Integer,Integer> map = IntStream.range(1,10).boxed().collect(Collectors.toMap(Function.identity(),i->i*i));
        System.out.println(map);
    }
}

Comments

[Misha]

IntStream only has the 3-argument collect. You should either rewrite your toMap in 3-arument form or convert IntStream to Stream<Integer> with .boxed()

[user1075613]

indeed, .boxed() was the key to success !