Algernon. Did you hear what I was playing, Lane?
Lane. I didn’t think it polite to listen, sir.
Algernon. I’m sorry for that, for your sake. I don’t play accurately—any one can play accurately—but I play with wonderful expression. As far as the piano is concerned, sentiment is my forte. I keep science for Life.
Wilde produces comic appeal through a number of literary devices, chief among which is ironic hyperbole. The quote above, the lines that open the play, are good examples of this. Irony is a literary trope that twists words or events around so that the ordinarily expected meaning or outcome is replaced by meaning or event that is not expected. Example: saying "Thank you so much," to someone who does not help you look for your prescription glasses.
Hyperbole is the rhetorical and literary device of exaggeration. Events and statements are made to appear of be larger than they are, more elaborate than they are. Wilde employs irony in combination with hyperbole to create comic effect and appeal.
In the lines above, Lane and Algernon are in adjoining rooms with open doors. What occurs in one room must surely be audible in the next room. Yet, when Algernon asks if Lane had heard his piano plying, Lane replies with an implied negative giving the excuse that he thought it would be impolite to listen. This is both ironic (how does one not listen to the piano played loudly in the adjoining room?!) and hyperbolic because it is an hyperbolic exaggeration of the standards of polite living. Thus a great start to a comedic play.
A particular forte in Wilde's repertoire of devices is that of logical fallacy. In the quote above, Algernon takes (1) pleasure in playing piano--an exact performance skill--inaccurately and (2) pride in being wonderfully expressive while inaccurate. As a result of Wilde's impeccable mastery of vocabulary and tone, the characters do say the most unlikely things in the most serious and straightforward of manners.
Algernon. ... may I dine with you to-night at Willis’s?
Jack. I suppose so, if you want to.
Algernon. Yes, but you must be serious about it. I hate people who are not serious about meals. It is so shallow of them.