Approach 2b: Use an Interface

Make an interface for ProfileFetcher
Pass that interface in the constructor for TradeCalculator
Construct the ProfileFetcher outside of TradeCalculator

public interface ProfileFetcher {
    public ProfileData fetchProfile(String userId);
}
public class SqlProfileFetcher implements ProfileFetcher {
    // ...
}
public class TradeCalculator {    
    private final ProfileFetcher profileFetcher;
    public TradeCalculator(ProfileFetcher profileFetcher) {
        this.profileFetcher = profileFetcher
    }
}

24 / 31