Hilchot Berachot 8:10-11 (When is saying the wrong beracha acceptable?)

If a person says the beracha of haadama on an apple, has he fulfilled his obligation? How about the beracha of haeitz on lettuce? What is the halacha if a person begins the beracha with the correct conclusion in mind, but says the wrong conclusion by mistake – must he repeat the beracha?