Java: Return the substring that is between the first and last appearance of the substring 'toast' in the given string, or return the empty string if substirng 'toast' does not exists

import java.util.*;

// Define a class named Main
public class Main {

    // Method to extract the middle of the bread based on certain conditions
    public String pickMiddleOfBread(String stng) {
        int len = stng.length(); // Get the length of the input string
        String tmpString = ""; // Initialize a temporary string variable
        String resultString = ""; // Initialize a result string variable
        int st = 0; // Initialize starting index
        int en = 0; // Initialize ending index
        boolean found = false; // Initialize a boolean variable indicating if "toast" is found

        // If the length of the input string is less than or equal to 10, return an empty string
        if (len <= 10)
            return "";

        // Iterate through the characters of the input string
        for (int i = 0; i < len - 4; i++) {
            tmpString = stng.substring(i, i + 5); // Extract a substring of length 5 starting at index 'i'

            // Check if the substring is "toast" and 'found' flag is true, update the ending index
            if (tmpString.equals("toast") && found == true)
                en = i;

            // Check if the substring is "toast" and 'found' flag is false, update the starting index and set 'found' flag to true
            if (tmpString.equals("toast") && found == false) {
                st = i + 5;
                found = true;
            }
        }

        // Extract the middle of the bread based on the starting and ending indices
        resultString = stng.substring(st, en);

        return resultString; // Return the result
    }

    // Main method to execute the program
    public static void main(String[] args) {
        Main m = new Main(); // Create an instance of the Main class

        String str1 = "sweettoastbuttertoast"; // Input string

        // Display the given string and the new string using pickMiddleOfBread method
        System.out.println("The given strings is: " + str1);
        System.out.println("The new string is: " + m.pickMiddleOfBread(str1));
    }
}