Chapter 3. Investigating DI

This chapter covers:

Learning about injection by setter and constructor
Investigating pros and cons of injection idioms
Identifying pitfalls in object graph construction
Learning about reinjecting objects
Discovering viral injection and cascaded object graphs
Learning techniques to inject sealed code

“The best way to predict the future is to invent it.”

Alan Kay

Previously we discussed two methods of connecting objects with their dependencies. In the main we have written classes that accept their dependencies via constructor. We have also occasionally used a single-argument method called a setter method to pass in a dependency. As a recap, here are two such examples from chapter 1:

public class Emailer {
    private SpellChecker spellChecker;

    public Emailer(SpellChecker spellChecker) {
        this.spellChecker = spellChecker;
    }
}

The same class accepting dependencies by setter:

public class Emailer {
    private SpellChecker spellChecker;

    public void setSpellChecker(SpellChecker spellChecker) {
        this.spellChecker = spellChecker;
    }
}

These are two common forms of wiring. Many dependency injectors also support other varieties and bias toward or away from these idioms.

Chapter 3. Investigating DI

This chapter covers:

3.1. Injection idioms

3.2. Choosing an injection idiom

3.3. Not all at once: partial injection

3.4. Injecting objects in sealed code

3.5. Summary

Chapter 3. Investigating DI

This chapter covers:

3.1. Injection idioms

3.2. Choosing an injection idiom

3.3. Not all at once: partial injection

3.4. Injecting objects in sealed code

3.5. Summary

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