Convert int stream to map

问题

I have an int stream 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?

回答1:

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);
    }
}

来源：https://stackoverflow.com/questions/38318181/convert-int-stream-to-map

标签

java-8