Adapter Design Pattern in Java
Connect incompatible interfaces so existing classes can work together.
What is Adapter?
Adapter acts like a translator. It wraps an existing class and exposes the interface that the client expects.
Beginner-friendly Java example
The following example shows the central idea of this pattern in a small, practical scenario.
interface PaymentProcessor {
void pay(double amount);
}
class LegacyGateway {
void makePayment(double value) {
System.out.println("Paid: " + value);
}
}
class GatewayAdapter implements PaymentProcessor {
private final LegacyGateway gateway = new LegacyGateway();
public void pay(double amount) {
gateway.makePayment(amount);
}
}Benefits and trade-offs
Benefits
- Separates responsibilities clearly.
- Improves flexibility as the application grows.
- Encapsulates structural complexity.
Trade-offs
- Can introduce extra wrapper classes.
- Choose the pattern only when the complexity is real.
When should you use it?
- Integrating a legacy library
- Wrapping a third-party API
- Converting data between formats
Key takeawayConnect incompatible interfaces so existing classes can work together. Start with the smallest structure that solves the coupling or composition problem.