Using JDK 8 Streams to Convert Between Collections of Wrapped Objects and Collections of Wrapper Objects

package dustin.examples.jdk8.streams;

import java.util.Objects;

/**
 * Basic characteristics of a motion picture.
 *
 * @author Dustin
 */
public class Movie
{
   /** Title of movie. */
   private final String title;

   /** Year of movie's release. */
   private final int yearReleased;

   /** Movie genre. */
   private final Genre genre;

   /** MPAA Rating. */
   private final MpaaRating mpaaRating;

   /** imdb.com Rating. */
   private final int imdbTopRating;

   public Movie(final String newTitle, final int newYearReleased,
                final Genre newGenre, final MpaaRating newMpaaRating,
                final int newImdbTopRating)
   {
      this.title = newTitle;
      this.yearReleased = newYearReleased;
      this.genre = newGenre;
      this.mpaaRating = newMpaaRating;
      this.imdbTopRating = newImdbTopRating;
   }

   public String getTitle()
   {
      return this.title;
   }

   public int getYearReleased()
   {
      return this.yearReleased;
   }

   public Genre getGenre()
   {
      return this.genre;
   }

   public MpaaRating getMpaaRating()
   {
      return this.mpaaRating;
   }

   public int getImdbTopRating()
   {
      return this.imdbTopRating;
   }

   @Override
   public boolean equals(Object other)
   {
      if (!(other instanceof Movie))
      {
         return false;
      }
      final Movie otherMovie = (Movie) other;
      return   Objects.equals(this.title, otherMovie.title)
            && Objects.equals(this.yearReleased, otherMovie.yearReleased)
            && Objects.equals(this.genre, otherMovie.genre)
            && Objects.equals(this.mpaaRating, otherMovie.mpaaRating)
            && Objects.equals(this.imdbTopRating, otherMovie.imdbTopRating);
   }

   @Override
   public int hashCode()
   {
      return Objects.hash(this.title, this.yearReleased, this.genre, this.mpaaRating, this.imdbTopRating);
   }

   @Override
   public String toString()
   {
      return "Movie: " + this.title + " (" + this.yearReleased + "), " + this.genre + ", " + this.mpaaRating + ", "
            + this.imdbTopRating;
   }
}

package dustin.examples.jdk8.streams;

/**
 * Wraps a movie like a Decorator or Adapter might.
 * 
 * @author Dustin
 */
public class MovieWrapper
{
   private Movie wrappedMovie;

   public MovieWrapper(final Movie newMovie)
   {
      this.wrappedMovie = newMovie;
   }

   public Movie getWrappedMovie()
   {
      return this.wrappedMovie;
   }

   public void setWrappedMovie(final Movie newMovie)
   {
      this.wrappedMovie = newMovie;
   }

   public String getTitle()
   {
      return this.wrappedMovie.getTitle();
   }

   public int getYearReleased()
   {
      return this.wrappedMovie.getYearReleased();
   }

   public Genre getGenre()
   {
      return this.wrappedMovie.getGenre();
   }

   public MpaaRating getMpaaRating()
   {
      return this.wrappedMovie.getMpaaRating();
   }

   public int getImdbTopRating()
   {
      return this.wrappedMovie.getImdbTopRating();
   }

   @Override
   public String toString()
   {
      return this.wrappedMovie.toString();
   }
}

With the Movie and MovieWrapper classes defined above, I now look at converting a collection of one of these into a collection of the other. Before JDK 8, a typical approach to convert a collection of Movieobjects into a collection of MovieWrapper objects would to iterate over the source collection of Movieobjects and add each one to a new collection of MovieWrapper objects. This is demonstrated in the next code listing.

// movies previously defined as Set<Movie>
final Set<MovieWrapper> wrappedMovies1 = new HashSet<>();
for (final Movie movie : movies)
{
   wrappedMovies1.add(new MovieWrapper(movie));
}

With JDK 8 streams, the operation above can now be implemented as shown in the next code listing.

// movies previously defined as Set<Movie>
final Set<MovieWrapper> wrappedMovies2 =
   movies.stream().map(movie -> new MovieWrapper(movie)).collect(Collectors.toSet());

Converting the other direction (from collection of wrapper objects to collection of wrapped objects) can be similarly compared to demonstrate how JDK 8 changes this. The next two code listings show the old way and the JDK 8 way.

final Set<Movie> newMovies1 = new HashSet();
for (final MovieWrapper wrappedMovie : wrappedMovies1)
{
   newMovies1.add(wrappedMovie.getWrappedMovie());
}

final Set<Movie> newMovies2 =
   wrappedMovies2.stream().map(MovieWrapper::getWrappedMovie).collect(Collectors.toSet());