CODEWITHSUNDEEP
javaspringdependency-injection
PenguinEngineer
PenguinEngineer

Reputation: 294

Dependency Injection: Spring and Java

I recently started to use the Spring Framework. In a book I found this example:

public class DamselRescuingKnight implements Knight {

   private RescueDamselQuest quest;

   public DamselRescuingKnight() {
      this.quest = new RescueDamselQuest();
   }

   public void embarkOnQuest() {
      quest.embark();
   }
}

Using Spring Constructor Dependency Injection, the example becomes:

public class DamselRescuingKnight implements Knight {

   private Quest quest;

   public DamselRescuingKnight(Quest quest) {
      this.quest = quest;
   }

   public void embarkOnQuest() {
      quest.embark();
   }
}

While the xml file configuration is:

<bean id="knight" class="com.springinaction.knights.DamselRescuingKnight">
   <constructor-arg ref="quest" />
</bean>

<bean id="quest" class="com.springinaction.knights.somethingThatImplementsQuest">
</bean>

In order to completely understand the concept, could you write an alternative example of Dependency Injection of the same classes using only Java (without Spring, so without the xml file)?

Upvotes: 1

Views: 253

Answers (1)

Wojtek
Wojtek

Reputation: 1308

This is equivalent to the dependency injection from your configuration file. The only difference is that your Quest object is created after the BraveKnight instance.

public class BraveKnight {
    private Quest quest;
    public BraveKnight(Quest quest) {
        this.quest = quest;
    }
}

public class Quest {

}

public class Main {
    public static void main (String[] args) {
        Quest quest = new Quest();
        BraveKnight knight = new BraveKnight(quest);
    }
}

Upvotes: 2

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