Backspace problem

Backspace problem
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Given a string consisting of lower case characters and hashes(#) where each hash represents a back space .
Find the resultant string after removing the backspaces from the given input string.
(Note : there will be no condition where we use backspace on empty string )
Example :
Input: xy#z
Output: xz

code in java    *************************************


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

public class Solution {

    static String backspace(String str) {
        StringBuilder sb = new StringBuilder();

        for (int i = 0; i < str.length(); i++) {
            char ch = str.charAt(i);

            if (ch == '#') {
                if (sb.length() > 0)
                    sb.deleteCharAt(sb.length() - 1);
            } else {
                sb.append(ch);
            }     
        }

        return sb.toString();
    }

    static boolean backspaceCompare(String S, String T) {
        
        if (S.equals(T))
            return true;
        return backspace(S).equals(backspace(T));
    }
    static boolean backspaceCompare0(String S, String T) {
        Stack<Character> sStack = new Stack<Character>();
        Stack<Character> tStack = new Stack<Character>();
        for (char ch : S.toCharArray()) {
            if (ch != '#')
                sStack.push(ch);
            else if (!sStack.isEmpty())
                sStack.pop();
        }
        for (char ch : T.toCharArray()) {
            if (ch != '#') 
                tStack.push(ch);
            else if (!tStack.isEmpty())
                tStack.pop();
        }

        return sStack.equals(tStack);
    }
    static boolean backspaceCompare1(String S, String T) {
        if (S == null && T == null)
            return true;
        else if (S == null || T == null)
            return false;
        else if (S.length() == 0 && T.length() == 0)
            return true;
        else if (S.length() == 0 || T.length() == 0)
            return false;
        int s       = S.length() - 1;
        int t       = T.length() - 1;
        int delete  = 0;
        for ( ; s >= 0 || t >= 0; ) {
            for (delete = 0; s >= 0 && S.charAt(s) == '#'; delete++, s--);
            for ( ; delete > 0 && s >= 0; s--, delete--) {
                if (S.charAt(s) == '#') {
                    delete++; s--;
                }
            }
            for (delete = 0; t >= 0 && T.charAt(t) == '#'; delete++, t--);
            for ( ; delete > 0 && t >= 0; t--, delete--) {
                if (T.charAt(t) == '#') {
                    delete++; t--;
                }
            }
            while (s >= 0 && t >= 0 && S.charAt(s) == T.charAt(t) && S.charAt(s) != '#') {
                s--; t--;
            }
            if (s >= 0 && t >= 0 && 
                S.charAt(s) != T.charAt(t) && 
                S.charAt(s) != '#' && T.charAt(t) != '#')
                return false;
        }

        
        return (s == t);
    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String S = sc.nextLine().trim();
        String T = sc.nextLine().trim();
        sc.close();
        System.out.print("main <<<      ");
        for (int i = 0; i < S.length(); i++)
            System.out.print("" + i);
        System.out.println();

        System.out.println("main <<< S ==>" + S + "<==");
        System.out.println("main <<< T ==>" + T + "<==");

        System.out.print("main <<<      ");
        for (int i = 0; i < T.length(); i++)
            System.out.print("" + i);
        System.out.println();
        System.out.println("main <<< backspaceCompare0: " + backspaceCompare0(S, T));
        System.out.println("main <<< backspaceCompare1: " + backspaceCompare1(S, T));
        System.out.println("main <<<  backspaceCompare: " + backspaceCompare(S, T));
    }
}