There is no StringBuffer constructor that accepts a char. What happens here is that Java has made a widening primitive conversion to transform the char into an int and then a StringBuffer with initial capacity of 77 was created.
But, there is a constructor that accepts a String and you can use it to solve your problem:
StringBuffer buffer = new StringBuffer("M");
Anyway, it is also recommended that you use StringBuilder, which is designed to be faster drop-in replacement for StringBuffer in places where the string buffer was being used by a single thread.
