The method setTitle(String) in the type Frame is not applicable for the arguments (float)

frame.setTitle() works in setup() for me, in 2.0.

md_za6, you need to convert the integer to a string:

1. void setup()
2. {
3.   size(500, 200);
4.   frame.setTitle("Sketch");
5. }
6. int c;
7. void draw()
8. {
9.   frame.setTitle(str(frameRate));
10.   line(c, 0, c, height);
11.   c++;
12. }

It is a bit "hysterical" this way, perhaps showing the frame rate one frame out of ten is enough:
if (frameCount % 10 == 0) frame.setTitle(str(frameRate));
Example:

1. void setup()
2. {
3.   size(500, 200);
4.   frame.setTitle("Sketch");
5.   frameRate(500);
6. }
7.  
8. int c;
9. void draw()
10. {
11.   if (frameCount % 50 == 0) frame.setTitle(str(frameRate));
12.   line(c, 0, c, height);
13.   c++;
14.   if (c >= width)
15.   {
16.     stroke(random(256));
17.     c = 0;
18.   }
19. }

It's funny I've never encountered this error w/ setTitle().

" Also, "" + variable or variable + "", replaces str(variable)."
Yes but concatenation of strings creates behind the scene a StringBuffer:

1. StringBuffer b = new StringBuffer("");
2. b.append(variable);
3. return b.toString();

while str(variable) involves only String.valueOf(variable);

I thought Processing's own convert functions did much more than Java's!

You have one str() version per type of argument... The simpler types just call String.valueOf(), while the arrays are managed with a loop.

" besides being a built-in Java feature, it skips calling a function"
The function call is probably optimized away by the Jit compiler, anyway. And being "built-in" doesn't mean it is fast: the concatenation creates object to collect later, as show, etc. That's why it is recommended to use a StringBuilder instead of using + in a loop.

" str() is aesthetically better"
Hey, at least we agree on this point! "" + v feels old school... And str() carries the intent, while "" + v is more obscure.
Note also that String.valueOf() can cache the result (IIRC), so it can be really fast (although perhaps it is only true for integers).