Collections.sort(List <T> list) & compareTo(T o)?

[Dillinger4]

I am a bit confused on how the sort method of the Collections class uses compareTo. Say for instance there is a compareTo() method which takes Alpha objects as a parameter. Is the letter of the first element being compared to the second elements letter field? Also when the value of i is printed out to the console it's not 0,1 0r -1.

public int compareTo(Alpha a){
int i = letter.compareTo(a.letter);
 return i;
}

The Alpha objects just have a field named letter which is a String type.

List<Alpha> alpha = new ArrayList<Alpha>(); 
 alpha.add(new Alpha("z"));
 alpha.add(new Alpha("g")); 
 alpha.add(new Alpha("k")); 
 alpha.add(new Alpha("q")); 
 alpha.add(new Alpha("a")); 
 alpha.add(new Alpha("b"));
 alpha.add(new Alpha("o")); 
 alpha.add(new Alpha("v")); 
 alpha.add(new Alpha("c"));

 Collections.sort(alpha); 
 System.out.println(alpha);