Alpha Nesting - Java Pt. 3

/*
* Purpose: to create a class which will check for alphabetical order within a hierarchy of a file
*/

import java.io.File;
import java.io.FileNotFoundException;
import java.util.*;

public class AlphaNest {

private Scanner sc; // stores the scanner object
private Stack stck; // the stack which is used to store lines of the file

//constructor passing in the name of the file to be working with
public AlphaNest(String fName){

sc = null;

//try catch used to create a Scanner which read in from a file
try{

sc = new Scanner(new File(fName));

}catch(FileNotFoundException e){

System.out.println("File could not be found");
System.exit(-1);

}//end try catch block

stck = new Stack();

}//end constructor

//determines if the file is alphabetized according to its hierarchy
public void checkAlpha(){

String space = ""; // stores the number of proceeding spaces of a level in the form of a string
String line = ""; //to store each line of the file one at a time
String trimLine = ""; // to store each line of the file without its proceeding white space
int numSpace = 0, prevNumSpace = 0; // stores the number of spaces before a level in the form of an integer for both the current line and the line on the top of the stack

//traverses file
while(sc.hasNext()){

line = sc.nextLine(); //each line of the file one at a time

//checks if the line is empty
if(line.length() > 0){

space = level(line);
numSpace = space.length();
prevNumSpace = 0;

//checks if the stack is empty
if(!stck.isEmpty())
prevNumSpace = stck.peek().length();

trimLine = line.trim();

//traverse the stack until the top line is on the same level as the current line read in from the file
while(numSpace < prevNumSpace){

stck.pop();
stck.pop();

prevNumSpace = stck.peek().length();

}//end while

//checks if the current line from the file is on the same level as the last line from the file and that the stack is not empty
if(numSpace == prevNumSpace && !stck.isEmpty()){

stck.pop();
String oldWord = stck.pop();

//checks if the two lines are in alphabetical order
if(trimLine.compareTo(oldWord) < 0){

System.out.println(oldWord + "\n" + trimLine);
System.exit(-1);

}//end if

}//end if

stck.push(trimLine);
stck.push(space);

}//end if

}//end while

System.out.println("The File is properly Alpha - Nested.");

}//end checkAlpha

//helper method to return a string representation of the level which the line of the file lies
private String level(String line){

String toRet = ""; //stores string to be returned
int i = line.length() - line.trim().length(); //stores the different in length between the line and the line without white space

//checks if the string to be returned needs to be modified
if(i > 0)
//loops until the string to return is the correct length in spaces
for (int n = i ; n > 0 ; n--)
toRet += " ";

return toRet;

}//end level

}//end AlphaNest