For my programming course at University of Berne I had to shortly talk about dependencies and how we handle them. I features some Inversion of Control methods and the DI framework Guice from Google.

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
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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
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4. Why are dependencies bad?
- well that depends...
 What are key features of 'good code'?
 Testable
 Modular
 Changable
 …
 Imagine that for huge applications...
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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
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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)
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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
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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;
}
}
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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);
}
}
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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())
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11. Improvements
- there's always a way to code better
 Use annotions that are provided by Guice
 @named
 @singelton
 Merge modules
 Merge providers
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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
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13. Questions
- experiences, smart remarks, suggestions
Joel Krebs
joel.krebs@students.unibe.ch
@jomikr on
www.aleaiactaest.ch
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