Dependency Injection

a common IoC approach

http://martinfowler.com/bliki/InversionOfControl.html

http://www.martinfowler.com/articles/injection.html

Inversion of Control

  #ruby
  puts 'What is your name?'
  name = gets
  process_name(name)
  puts 'What is your quest?'
  quest = gets
  process_quest(quest)

  require 'tk'
  root = TkRoot.new()
  name_label = TkLabel.new() {text "What is Your Name?"}
  name_label.pack
  name = TkEntry.new(root).pack
  name.bind("FocusOut") {process_name(name)}
  quest_label = TkLabel.new() {text "What is Your Quest?"}
  quest_label.pack
  quest = TkEntry.new(root).pack
  quest.bind("FocusOut") {process_quest(quest)}
  Tk.mainloop()

Dependency Injection

Explanation

A naive example

class MovieLister…
  public Movie[] moviesDirectedBy(String arg) {
      List allMovies = finder.findAll();
      for (Iterator it = allMovies.iterator(); it.hasNext();) {
          Movie movie = (Movie) it.next();
          if (!movie.getDirector().equals(arg)) it.remove();
      }
      return (Movie[]) allMovies.toArray(new Movie[allMovies.size()]);
  }

A naive example

public interface MovieFinder {
    List findAll();
}

class MovieLister…
  private MovieFinder finder;
  public MovieLister() {
    finder = new ColonDelimitedMovieFinder("movies1.txt");
  }