A Comparable would be a String -- it comes with a default sort order (A, B, C, D, E, ...)
A comperable would be a class that you write to implement sorting on non-Comparable objects, or to provide sorting other than the default of a Comparable object.
For example, say that I decided that I wanted to "alphabetize" a collection of string not be the standard Roman alphabet but by the "QWERTY" keyboard alphabet. I would write a Comperable object to do this.
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(This is an example that comes to mind because my three-year-old son now sings, to the tune of "Twinkle, Twinkle, Little Star"/"The Alphabet Song" :
"Q W E R T Y,
U I O P A S D.
F G H J K L Z.
X C V B N and M.
Now I know ny keyboard keys,
Next time won't you sing with me...."
of course, I made sure that he knows that alphabet both ways...
)