StreamEtude.java

import java.util.concurrent.*;
import java.util.Arrays;
import java.util.stream.Collectors;

public class StreamEtude{
  public static void main (String[] args) {
    ExecutorService exe = Executors.newFixedThreadPool(4);
    Arrays.stream(args)
      .map(Integer::parseInt)
      .map( arg -> exe.submit(() -> fib(arg)) ).collect(Collectors.toList()).stream()
      .forEach( result -> {
        try{System.out.println(result.get());}
        catch(Exception ex){throw new RuntimeException(ex);}
      });
    exe.shutdown();
    
    // 上と同じような動作
    Arrays.stream(args).parallel().map(Integer::parseInt).map(StreamEtude::fib)
      .collect(Collectors.toList()).stream()
      .forEach(System.out::println);
  }

  static int fib(int x){
    System.out.println(String.format("Called fib(%d)", x));
    return fib_(x);
  }

  static int fib_(int x){
    if (x == 0 || x == 1) return x;
    return fib_(x-1) + fib_(x-2);
  }
}