Proxy

Imagine fetching a heavy user profile from a database. You use a Proxy to delay that expensive database call until the exact moment you actually need the data (Lazy Loading).

public interface UserRepository {
    String getUserData();
}

1. The real, heavy database call

public class RealUserRepository implements UserRepository {

    public RealUserRepository() {
        System.out.println("Connecting to DB... (Heavy operation)");
    }
    public String getUserData() { return "User Data from DB"; }
}

2. The PROXY (Controls access)

public class UserRepositoryProxy implements UserRepository {
    private RealUserRepository realRepository;

    public String getUserData() {
        // Intercepting the call! Only initialize if we absolutely have to.**
        if (realRepository == null) {
            realRepository = new RealUserRepository(); 
        }
        return realRepository.getUserData();
    }
}