main.java

public class main {
    public static void main(String[] args) {
        String str="hello world!";
        System.out.println(str.length());// this is count the character of the string 
        
        System.out.println(str.charAt(7));
        // this method is return the character at the inde position

        System.out.println(str.substring(7));
        // this method return the substring from the ith index caracter to end 

        System.out.println(str.substring(2,6));

      //Returns the substring from i to j-1 index.

      System.out.println(str.concat("saniya"));
     // Concatenates specified string to the end of this string

        System.out.println(str.indexOf('o'));
        /*Finds the position of the first occurrence of the given
         substring within the main string. If the specified string s is 
        not found in the input string, the method returns -1 by default. */


        System.out.println(str.indexOf('l',3));
        //Returns the index within the string of the first occurrence 
        // of the specified string, starting at the specified index.

        System.out.println(str.lastIndexOf('l', 3));

        /*Returns the index within the string of the last occurrence of the specified string.
      If the specified string s is not found in the input string, 
        the method returns -1 by default. */
    }
     
}