Creating a custom String Tokenizer

[kgrant5116]

I have been given a lab assignment where I am to write my own StringTokenizer class. I am having some trouble understanding the logic of how this is done. As my loop goes through the string one character at a time, it is supposed to determine if the character it is looking at is a delimiter or not. If it is a not delimiter then it looks at the character before it and if that character is a delimiter then it has found the start of a token and saves the index in an 'int' variable. Vice versa for the 'end' variable. I have been working on this for over a week and cannot come up with how this is done. The main contains 4 separate strings that each use this class to tokenize the string. I havnt even gotten the first one to work where it only has one space as the delimiter. Any suggestions on how I might be wrong in my logic?

class ST
{
    String star[];
    int numTokens;
    int index = 0;

    public ST(String s, String d)
    {
        star = new String[50];
        String str = s;
        int start = 0;
        int end = 0;
        numTokens = 0;
        String token;
        //String delim = d;
        for (int i = 1; i < str.length(); i++)
        {
            String t = str.substring(i, i + 1);
            String u = str.substring(i - 1, i);

            if (end != 0)
            {
                if (!t.equals(d))
                {
                    if (u.equals(d))
                    {
                        start = str.indexOf(t);
                    }
                }
            }
            if (t.equals(d))
            {
                if (!u.equals(d))
                {
                    end = str.indexOf(t);
                    token = str.substring(start, end);
                    star[index++] = token;
                    numTokens++;
                }
            }
          // System.out.println(token);
        }
    }

    public boolean isDelim(String s)
    {
        String delim = s;

        return delim.substring(0, 1).equals(" ");
    }

    public ST(String s)
    {
        this(s, " ");
    }

    public int countTokens()
    {
        return (numTokens - index);
    }

    public boolean hasMoreTokens()
    {
        return (numTokens > index);
    }

    public String nextToken()
    {
        return (star[index++]);
    }
}


public class Lab5
{

    public static void main(String argv[])
    {
        String str;

    //1)
        str = "Hello world";
        ST stok= new ST(str);

        System.out.println(str);

        while (stok.hasMoreTokens())
        {
            System.out.println("#tokens = " + stok.countTokens());
            System.out.println("token: " + stok.nextToken());
        }
        System.out.println("#tokens = " + stok.countTokens());
        System.out.println("\n\n");

    //2)
        str = "    Hello    world   ";
        stok= new ST(str);

        System.out.println(str);

        while (stok.hasMoreTokens())
        {
            System.out.println("#tokens = " + stok.countTokens());
            System.out.println("token: " + stok.nextToken());
        }
        System.out.println("#tokens = " + stok.countTokens());
        System.out.println("\n\n");

    //3)
        str = "root:x:0:0:root:/root:/bin/bash";
        stok = new ST(str, ":");

        System.out.println(str);

        System.out.println("username = " + stok.nextToken());
        System.out.println("password = " + stok.nextToken());
        System.out.println("userid   = " + stok.nextToken());
        System.out.println("groupid  = " + stok.nextToken());
        System.out.println("comment  = " + stok.nextToken());
        System.out.println("home dir = " + stok.nextToken());
        System.out.println("shell    = " + stok.nextToken());
        System.out.println("\n\n");

 //4)
        str = "Hello-world.It is!a nice day,today";
        stok= new ST(str,"-.!, ");

        System.out.println(str);

        while (stok.hasMoreTokens())
        {
            System.out.println("#tokens = " + stok.countTokens());
            System.out.println("token: " + stok.nextToken());
        }
        System.out.println("#tokens = " + stok.countTokens());
    }