🔍 What is Tight Coupling and Loose Coupling? (Android Developer Explanation)

✅ Tight Coupling

Two classes/components are tightly coupled when they depend on each other directly.
If one changes, the other must also change.
It reduces flexibility and reusability.

📌 Example (Bad Practice – Tight Coupling)

class UserRepository {
    fun getUser() = "Android Developer"
}

class UserViewModel {
    private val repository = UserRepository() // Direct object creation → TIGHT COUPLING

    fun printUser() {
        println(repository.getUser())
    }
}

🔴 Problems:

• UserViewModel cannot work without UserRepository

• Hard to unit test (cannot inject mock repo)

• If repository changes, viewmodel breaks

• Not reusable

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✅ Loose Coupling

Two classes are loosely coupled when they depend on abstractions (interfaces) instead of concrete classes.
You can replace dependency without modifying main logic → more flexible.

📌 Example (Good Practice – Loose Coupling with DI)

interface UserRepository {
    fun getUser(): String
}

class UserRepositoryImpl : UserRepository {
    override fun getUser() = "Android Developer"
}

class UserViewModel(private val repository: UserRepository) {
    fun printUser() {
        println(repository.getUser())
    }
}

✅ Benefits:

• You inject dependency, not create it

• Easier unit testing (can pass fake/mock repo)

• Supports dependency injection (Hilt, Koin, Dagger)

• Better for Clean Architecture

Unit Test Example:

class FakeRepo : UserRepository {
    override fun getUser() = "Test User"
}

val viewModel = UserViewModel(FakeRepo())

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🔁 Comparison Table

Feature	Tight Coupling	Loose Coupling
Flexibility	❌ Low	✅ High
Testability	❌ Hard	✅ Easy
Uses interface?	❌ No	✅ Yes
Dependency created inside class?	✅ Yes	❌ No (Injected)
Works well with DI (Hilt/Koin)?	❌ No	✅ Yes

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🏗 Real Android Example of Loose Coupling (Hilt)

@Module
@InstallIn(SingletonComponent::class)
object AppModule {
    @Provides
    fun provideUserRepo(): UserRepository = UserRepositoryImpl()
}

@HiltViewModel
class UserViewModel @Inject constructor(
    private val repository: UserRepository
) : ViewModel() {
    fun getUserName() = repository.getUser()
}

✅ ViewModel doesn’t know which implementation is injected
✅ Can switch to MockUserRepo() easily for testing
✅ Architecture-friendly

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💡 Simple Definition for Interview

Tight coupling = classes depend directly on each other
Loose coupling = classes communicate through interfaces or injected dependencies

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