Examples of idealism in Don Quixote?
Don Quixote's character is permeated by idealism. Though strictly speaking, that idealism is solely related to his persona as an errant knight rather than to the real Alonso Quixano underneath. In that sense, idealism is virtually synonymous with madness. But when Don Quixote throws off the mask of the knight, it is surprising just how much common sense and wisdom he appears to possess.
However, as a knight, Don Quixote is a complete idealist (or madman). Arguably the most famous example of this is when the Don charges at windmills, believing them to be ferocious giants. His knightly veneration of courtly love leads him to regard a couple of prostitutes outside an inn as ladies of quality. A similar episode takes place when he treats a couple of common goatherds like gentlemen, his social equals. In both of these examples, the Don's idealism, however deluded it may appear, leads to his connecting with people to whom he normally wouldn't give the time of day. There's a hint of satire here; Don Quixote's idealism sheds a revealing light on the conventional relations between different classes at that time in Spanish society.