working on my own string tokenizer project and would like a little guidance.

public class Lab6
{

    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());
    }
}
class ST
{
    String star[];
    int numtokens = 0;
    int index=0;

    public ST(String s, String d)
    {
        star = new String[50];
        String str = s;
        int start = 0;
        int end =0;
        int u = str.indexOf(' ');
        String c0;

        for(int i=0; i<str.length();>        {
            c0 = str.substring(i,i+2);
            System.out.println("[" + c0 +"]");

            String c1 = c0.substring(0,1);
            String c2 = c0.substring(1,2);
            System.out.println("[" + c1 + "]");
            System.out.println("[" + c2 + "]");

            if(c1 == " ")
            {
                if(c2 != " ")
                {
                start = i+2;
                }
            }
            if(c1 != " ")
            {
                if(c2 == " ")
                {
                end = i;
                }
            }

            if (end < start)
            {
                end = str.length();
            }
            star[numtokens] = str.substring(start,end);
            System.out.println("[" + star[numtokens] + "]");
            numtokens ++;

       }
    }

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

    public int countTokens()
    {
        return(numtokens - index);
    }
  public boolean hasMoreTokens()
    {
        return (index < numtokens);
    }

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