a simple google guice example

GoogleGuiceExample.java

import com.google.inject.AbstractModule;
import com.google.inject.Guice;
import com.google.inject.Inject;
import com.google.inject.Injector;

import javax.inject.Singleton;

public class MainApp {
  public static void main(String[] args) {
    Injector injector = Guice.createInjector(new AppInjector());
    MyController app = injector.getInstance(MyController.class); // at this moment the data was injected
    System.out.println(app.getDatabaseData());
  }
}

class MyController {
  @Inject //inject directly the property
  private Database db;
//  @Inject //injcting by param with setter methode. Or you can inject the data by contructor injection
//  public void readDatabaseData(Database db) {
//    this.db = db;
//  }
  public String getDatabaseData() {
    return db.getData();
  }
}

// configure which database should be used!
class AppInjector extends AbstractModule {
  @Override
  protected void configure() {
    bind(Database.class).to(InMemoryDatabase.class);
  }
}

interface Database {
  public String getData();
}

@Singleton
class InMemoryDatabase implements Database {
  @Override
  public String getData() {
    return "data from InMemoryDatabase";
  }
}

@Singleton
class MySqlDatabase implements Database {
  @Override
  public String getData() {
    return "data from MySqlDatabase";
  }
}

My pleasure