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.

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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