Histogram of letters in string
Throughout your code you use for loops.  Java 8 has been around for 4 years now. It is time you start using the new (now quite old) collection streams. Here are some snipets to get you started:

string.chars().forEach(letterThere -&gt; {
  ...
})

IntStream.rangeClosed('a', 'z').forEach(i -&gt; {
  ...
})

regarding whereInLetterCtr() : you advance comparisonLetter from 'a' to 'z' with the ++ operator so you realize that the letters form a sequence of numbers and that you can apply mathematical operations on them.
so...
instead of the whole loop you can get the result by doing letter - 'a'