Adapter

Wraps an incompatible interface so it can work with existing code without modification.

The Problem

You want to use a third-party library or legacy class, but its interface doesn't match what your code expects. You can't (or don't want to) modify either side.

How It Works

›Bridges two incompatible interfaces without changing their source code
›Object adapter wraps the instance (composition); class adapter uses inheritance
›The client only ever sees the target interface — not the adapted class
›Common when integrating third-party SDKs or legacy code
›Can adapt multiple adaptees if needed (multi-adapter)

When to Use

✓Using a third-party library with a different interface than what your code expects

✓Reusing legacy code that cannot be modified

✓Multiple classes with incompatible interfaces need to collaborate

✓Providing a stable interface while underlying implementations change

Real-World Examples

🍎

iOS

UITableViewDataSource & UICollectionViewDataSource adapting model arrays to views

🤖

Android

RecyclerView.Adapter adapting List<T> to RecyclerView cells

🌐

Web

Axios adapters (browser/node), ORM adapters for different databases

Code Examples

Swift

// Legacy payment SDK (cannot modify)
class LegacyPaymentSDK {
    func makePayment(amount: Double, cardNumber: String) -> Bool {
        print("Legacy: charging $\(amount) to \(cardNumber)")
        return true
    }
}

// Modern interface our app depends on
protocol PaymentProcessor {
    func process(amount: Double, method: String) -> Bool
}

// Adapter: wraps legacy to match our interface
class PaymentAdapter: PaymentProcessor {
    private let sdk = LegacyPaymentSDK()

    func process(amount: Double, method: String) -> Bool {
        sdk.makePayment(amount: amount, cardNumber: method)
    }
}

// App code only knows about PaymentProcessor
let processor: PaymentProcessor = PaymentAdapter()
processor.process(amount: 99.99, method: "4111-1111-1111-1111")