Implement the flatMap function on list<T>, which should be equivalent to list.stream().flatMap(f) - Java Lambda Stream

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Description

Implement the flatMap function on list<T>, which should be equivalent to list.stream().flatMap(f)

Demo Code


import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;

public class Main {

  /**/*from w w w.  jav  a  2s .c  o m*/
   * Implement the flatMap function on list<T>. The result should be equivalent to
   * the execution of the code:
   * 
   * <pre>
   * list.stream().flatMap(f).collect(Collectors.toList()) ; BUT YOU CANNOT USE
   * Stream API in this implementation.
   * 
   * @param list
   * @param f
   *          a function from T to List<R>
   * @return a list fo type list<R>
   */

  public static <T, R> List<R> flatMap(List<T> list, Function<? super T, List<R>> f) {
    // The result should be equivalent to the code:
    // list.stream().flatMap(f) ;
    List<R> rlt = new ArrayList<>();
    list.forEach(t -> f.apply(t).forEach(rlt::add));
    return rlt;
  }
}

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