This code is written just to enjoy the aliasing. If you type the same character at the same place, first in white color and then in black color on a black background for exemple, that gives rise to the so-called "antialiasing". The quality or the faults of this kind of new version of the font you are using depends on the definition of your screen. Paste the code and run with one another font.
If you set two same-sized boxes at exactly the same place in a 3D space with different values in fill() method for each box, no problem, Processing display only one cube filled with the last color commanded in the code. But if you add only one pixels to the size of one the boxes, very nice problems occur.