Brief introduction into dependencies
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The document discusses dependencies in object-oriented programming, highlighting their potential issues and the need for inversion of control to manage them. It details how to implement dependency injection using frameworks like Guice, including the use of providers and modules for object creation. While emphasizing the benefits of reducing dependencies for code quality, it cautions against using such frameworks for small applications.
![The Provider
- let's just copy & paste
import com.google.inject.Inject;
import com.google.inject.Provider;
public class GameProvider implements Provider<Game> {
private Provider<IDie> dieProvider ;
@Inject
public GameProvider(Provider<IDie> dieProvider) {
this.dieProvider = dieProvider;
}
@Override
public Game get() {
Player[] players = { new Player("Jack"), new Player("Jill")};
Game game = new Game(12, players, dieProvider .get());
game.setSquareToLadder(2, 4);
game.setSquareToLadder(7, 2);
game.setSquareToSnake(11, -6);
game.setSquareToLargeSquare(4);
game.setSquareToTrapDoor(10, -6);
return game;
}
}
15.04.2011 Joel Krebs 8](https://image.slidesharecdn.com/dependencies-110415024747-phpapp01/85/Brief-introduction-into-dependencies-8-320.jpg)
Brief introduction into dependencies
- 1. Dependencies with and without Guice
- 2. Outline What are dependencies? How dependencies cause problems Inversion of Control and Hollywood Guice – the solution for everything (almost) Providers The creation of a new object 15.04.2011 Joel Krebs 2
- 3. What are dependencies? - or why not to code only one class Classes depends on others, that comes with Object orienteted programming (OOP) Dependencies are classes, that are used by other classes in order to work Example: Board Die Player 15.04.2011 Joel Krebs 3
- 4. Why are dependencies bad? - well that depends... What are key features of 'good code'? Testable Modular Changable … Imagine that for huge applications... 15.04.2011 Joel Krebs 4
- 5. Inversion of Control - what has Hollywood to do with all this? Inversion of Control (IoF) is a design pattern to reduce dependencies without any frameworks Difference to procedural architecture: Board Die Player Die Board Player 15.04.2011 Joel Krebs 5
- 6. Methods for Inversion of Control - something everybody can do General rules: Use interfaces Use getters and setters 1. Using factories IDie die = DieFactory.get() 2. Using constructors injection public Board(IPlayer player, IDie die) 3. Using setter injection public void setDie(IDie die) 15.04.2011 Joel Krebs 6
- 7. Guice - well, it works for Google, let's try Real dependency injection only works with frameworks (e.g. Guice, Spring) They can save you a lot of time and coding, but not for too small applications Guice needs you... ...to tell Guice wich Interface maps to which class => module ...to give him the necesarry information how to construct a object => Provider 15.04.2011 Joel Krebs 7
- 8. The Provider - let's just copy & paste import com.google.inject.Inject; import com.google.inject.Provider; public class GameProvider implements Provider<Game> { private Provider<IDie> dieProvider ; @Inject public GameProvider(Provider<IDie> dieProvider) { this.dieProvider = dieProvider; } @Override public Game get() { Player[] players = { new Player("Jack"), new Player("Jill")}; Game game = new Game(12, players, dieProvider .get()); game.setSquareToLadder(2, 4); game.setSquareToLadder(7, 2); game.setSquareToSnake(11, -6); game.setSquareToLargeSquare(4); game.setSquareToTrapDoor(10, -6); return game; } } 15.04.2011 Joel Krebs 8
- 9. The Module - different modules for testing and use package snakes; import com.google.inject.AbstractModule; public class SnakesModule extends AbstractModule { @Override protected void configure() { bind(IDie.class) .to(Die.class); bind(Game.class) .toProvider(GameProvider.class); } } public class SnakesTestModule extends AbstractModule { @Override protected void configure() { bind(IDie.class) .toInstance(context.mock(IDie.class)); bind(Game.class) .toProvider(GameProvider.class); } } 15.04.2011 Joel Krebs 9
- 10. How we get new objects - all roads lead to Rome...or a game So if I want a board game, what happens? Main method Injector.getInstance(Game.class) SnakesModule bind(Game.class) .toProvider(GameProvider.class) GameProvider new Game(... dieProvider.get()) 15.04.2011 Joel Krebs 10
- 11. Improvements - there's always a way to code better Use annotions that are provided by Guice @named @singelton Merge modules Merge providers 15.04.2011 Joel Krebs 11
- 12. Conclusions - doesn't make it all more complicate? Reduce dependencies in general improves your code in many ways It needs a certain kind of mindset, but you get used to it Frameworks like Guice can improve your code as well and may save you a lot of time But I would not use them for too small projects 15.04.2011 Joel Krebs 12
- 13. Questions - experiences, smart remarks, suggestions Joel Krebs joel.krebs@students.unibe.ch @jomikr on www.aleaiactaest.ch 15.04.2011 Joel Krebs 13