Interfaces vs Abstract Classes in Unity: Which One Is Better?

Here we go again, yet another blog post about a debate that's been quietly ruining developer's sleep since the dawn of object-oriented programming. Sit back and relax, because we're finally settling the "interface or abstract class" argument. 

Why This Comparison Even Matters

As a solo game developer like myself, you don't have a senior architect looking over your shoulder telling you your class hierarchy is a big mess. When it comes to interfaces vs abstract classes in Unity, the choice you make on day one tends to snowball... and it'll either be a clean, swappable system, or turn into a tangled inheritance chain you'll be untangling weeks from now. Fully understanding both of them is important, especially at the beginners stage, since this is not even an intermediate topic.

Both let you enforce structure across your scripts. Neither is "wrong." But picking the wrong one for the wrong job is how you end up with an Enemy abstract class that fifteen unrelated objects are awkwardly pretending to inherit from just to get one shared method.

 

The Two Contenders, Briefly

• Interface; see it as a contract. It says "that's fine that you use me, BUT any class that implements me must have the SAME methods otherwise I'll throw an error - and a tantrum!" However, it provides no shared code or fields of its own.
• Abstract class; is just a partially-built base class. It can hold real fields, real shared logic, and force subclasses to fill in the rest via abstract methods. 

Here's the relationship in a nutshell:

Interface; defines what a class can do and an abstract class; defines what a class is.

That one-liner will save you more headaches than any 40-minute YouTube tutorial on SOLID principles. Let that sink in, and when you're ready - let's move on.

 

Interfaces: Built for Unrelated Objects, One Shared Ability

If you're wondering when to use interfaces in Unity C#, the short answer is: whenever multiple unrelated objects need to share a capability, but otherwise have nothing in common.

Classic example; damage systems. Your player can take damage. So can a crate. So can a turret. So can a barrel that explodes dramatically because explosions are fun. These objects share no inheritance relationship, but they all need a TakeDamage(int amount) method.

public interface IDamageable
{
    void TakeDamage(int amount);
}

Now PlayerController, ExplosiveBarrel, and TurretEnemy can all implement IDamageable without being forced into some awkward shared parent class that makes no logical sense (a barrel is not a turret, and frankly, it shouldn't have to pretend to be).

Interfaces also solve a hard C# limitation: no multiple inheritance for classes, but unlimited interface implementation. So if your enemy needs to be IDamageable, IStunnable, and IPoisonable all at once, interfaces are the only clean way to pull that off which is exactly why when to use interfaces in Unity C# so often comes down to "capability stacking."

 

Abstract Classes: Built for Shared Code Across a Family of Objects

When you're weighing abstract class vs interface for game architecture, the deciding factor usually comes down to one question: do these objects share actual behavior, or just a shared label?

Abstract classes shine when you've got a genuinely related family of objects that can share real code. Think enemy types in a top-down shooter — GoblinEnemy, SkeletonEnemy, and OrcEnemy all need movement logic, a health system, and a basic attack pattern. They're just flavored differently.

public abstract class Enemy : MonoBehaviour
{
    public int health = 100;

    public virtual void TakeDamage(int amount)
    {
        health -= amount;
        if (health <= 0) Die();
    }

    protected abstract void Die();
}

TakeDamage is shared logic here because every enemy loses health the same way. Die() is abstract, so each enemy type defines its own death behavior. That's the power move of abstract classes: shared code where it makes sense and forced customization where it doesn't.

Watch out for the trap a lot of solo developers fall into: using an abstract class purely to define required methods, without sharing any actual logic. Do that, and you've just reinvented an interface with the added downside that a class can only inherit from one abstract class at a time.

 

API Comparison: What Actually Changes in Code

Here's the part I actually care about; how much does code structure actually change?

Interface-based
public interface IDamageable { void TakeDamage(int amount); }
public class Player : MonoBehaviour, IDamageable { ... }
public class ExplosiveBarrel : MonoBehaviour, IDamageable { ... }

Abstract-class-based
public abstract class Enemy : MonoBehaviour { ... }
public class Goblin : Enemy { ... }
public class Skeleton : Enemy { ... }

With interfaces, unrelated MonoBehaviours bolt on a capability side-by-side. With abstract classes, related objects sit in a single inheritance line and share a base. That structural difference is really the whole decision in miniature side-by-side capabilities vs. a shared trunk with branches.

 

So Which One Should You Actually Use?

Here's the honest, no-fluff answer for a solo developers making an interfaces vs abstract classes in Unity call on a deadline:

• Unrelated objects, one shared ability (damage, interaction, pickup) → Interface.
• Objects need more than one shared ability at once (damageable AND stunnable AND poisonable) → Interface, possibly several stacked.
• Related objects that share real code (movement, health, shared attack logic) → Abstract class.
• You want default behavior subclasses can override → Abstract class, using virtual methods.
• Project's still young and you're not sure yet → Start with an interface. It's easier to add an abstract class later than to untangle a bloated inheritance chain.

That last point matters more than people admit. Interfaces are cheap to add and don't lock you into a hierarchy. Abstract classes are a bigger commitment, refactoring out of one later, once ten scripts depend on it, is not a fun Saturday.

Can You Use Both? (Yes, and You Probably Should)

This is the part that trips people up most in the abstract class vs interface for game architecture conversation: it's not actually either/or. Plenty of well-structured Unity projects use both, together. In fact, I recommend it.

A perfect example would be my own game I'm working on at this time of writing: Anomaly Hours: Forest Cabin. All anomalies have a base class with shared data in it. Every anomaly has a 'test option', 'score value', 'if the anomaly is active or not' etc. Then the classes like AnomalyRotation, AnomalyMaterial etc, inherit from BaseAnomaly. A raycast detects whether or not the component has a BaseAnomaly attached to it and if it's active.

Then, I have an interface to increase performance with an update publisher. Basically what this does is I use 1 (one!) update method for the entire game. I wrote an article about this technique that you can read here.

 

Click image to zoom in.

 

Wrapping Up

None of these two is objectively "wrong", used them to solve different problems. If you're sharing real code across a related family of objects, reach for an abstract class. If you're promising a capability across unrelated objects, reach for an interface. 

For more info about Interfaces read this article on Microsoft Learn. 

For more insight about Abstract Classes, read this article on Microsoft Learn. 

 

~happy Coding!