/* package whatever; // don't place package name! */
 
import java.util.*;
import java.util.stream.*;
import java.util.function.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone {
  public static<R,U> List<R> myMap(Stream<U> s, Function<U,R> fnctn) {
    return s.reduce(
      new ArrayList<R>(),
      (List<R> list, U elem) -> { list.add(fnctn.apply(elem)); return list; },
      null
    );
  }
 
  public static void main (String[] args) throws java.lang.Exception {
    List<String> words = Arrays.asList("word1", "word2", "word3");
    System.out.println(myMap(words.stream(), s->Integer.valueOf(s.substring(s.length()-1))));
  }
}

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