Factory Pattern

Decouple 'what' from 'how it's built'

A factory method returns an interface type while deciding internally which concrete class to instantiate. Callers never call new ConcreteThing() directly, so a new implementation can be added without touching client code.

A payment factory

The factory centralises the if/switch that picks an implementation — that logic exists exactly once instead of being copy-pasted at every call site.

interface PaymentGateway { void charge(int cents); }

class PaymentGatewayFactory {
    static PaymentGateway create(String provider) {
        return switch (provider) {
            case "stripe" -> new StripeGateway();
            case "paypal" -> new PayPalGateway();
            default -> throw new IllegalArgumentException(provider);
        };
    }
}

PaymentGateway gw = PaymentGatewayFactory.create("stripe");
gw.charge(500);