I dont Know What the error mean and what the wrong with the code !! I appreciate if someone explain it for me =)


import java.io.File;
import java.io.FileNotFoundException;

import java.util.Scanner;
import java.util.Stack;

public class Telenum {

    public static int num(char s) {
        int y = 0;
        if ((s == 'i') || (s == 'j')) {
            y = 1;
        }
        if ((s == 'a') || (s == 'b') || (s == 'c')) {
            y = 2;
        }
        if ((s == 'd') || (s == 'e') || (s == 'f')) {
            y = 3;
        }
        if ((s == 'g') || (s == 'h')) {
            y = 4;
        }
        if ((s == 'k') || (s == 'l')) {
            y = 5;
        }
        if ((s == 'm') || (s == 'n')) {
            y = 6;
        }
        if ((s == 'p') || (s == 'r') || (s == 's')) {
            y = 7;
        }
        if ((s == 't') || (s == 'u') || (s == 'v')) {
            y = 8;
        }
        if ((s == 'w') || (s == 'x') || (s == 'y')) {
            y = 9;
        }
        if ((s == 'o') || (s == 'q') || (s == 'z')) {
            y = 0;
        }
        return y;

    }

    public static void main(String[] args) throws FileNotFoundException {

        Scanner sc = new Scanner(new File("pp"));
        String phonum = "", w1, w2 = null,l="", word = "";
        int wn = 0, numtr, phnum, flag;
        boolean f = true;
        char Takechar = ' ';
        Stack st1 = new Stack();
        Stack st2 = new Stack();
        while (f != false) {

            phonum = "" + sc.next();

            if (phonum.equals("-1")) {
                break;
            }
            wn = sc.nextInt();
if ((phonum.length()<=100)&&(wn<=50000)){
            for (int i = 0; i < wn; i++) {
                l=sc.next();
                if (l.length()<51){
                st1.add(l);}else{break;}
            }

            //transfare word to num
            for (int i = 0; i < st1.size(); i++) {
                word = (String) st1.get(i);


                flag = word.length();
                for (int j = 0; j < word.length(); j++) {
                    Takechar = word.charAt(j);
                    numtr = num(Takechar);


                    phnum = phonum.charAt(j) - '0';


                    if (numtr != phnum) {

                        break;
                    }

                    flag--;
                    if (flag == 0) {
                        st2.add(word);

                        w1 = phonum.substring(word.length());
                        phonum = "" + w1;
                    }
                }
            }
            if (st2.empty()) {
                System.out.println("no solution.");
                st1.clear();
            } else {

                for (int s = 0; s < st2.size(); s++) {
                    System.out.print(st2.get(s) + " ");

                }
                System.out.println();
                st2.clear();
                st1.clear();

            }

        }
    }
    }
}