I can't recommend Effective Java enough. Even if one hates Java with passion. I haven't managed to find a better book on how to design an API in any language. I

I can't recommend Effective Java enough. Even if one hates Java with passion. I haven't managed to find a better book on how to design an API in any language. It learned me to think about the consumers of my code all the time (even if I'm the only author on a given project) The chapters on exceptions, defensive coding, generics are brilliant. The whole book is written in an effective manner. Dense with information, short and still readable. The second best: Eloquent Ruby. Brilliantly written and mature. Instead of hyping everything up, the author elaborates the downsides of each described technique and power tool.