Chatpt.java

 public class Chatpt {
    public static void main(String[] args) {

        String str = "hello wirld!";
        String str2 = "HELLO WIRLD!";
        String str3 = "hello";

        // length()
        System.out.println("Length: " + str.length());

        // charAt()
        System.out.println("Character at index 1: " + str.charAt(1));

        // substring(i)
        System.out.println("Substring from index 6: " + str.substring(6));

        // substring(i, j)
        System.out.println("Substring from 0 to 5: " + str.substring(0, 5));

        // concat()
        System.out.println("Concat: " + str.concat(" Welcome"));

        // indexOf()
        System.out.println("Index of 'o': " + str.indexOf("o"));

        // indexOf(s, i)
        System.out.println("Index of 'o' from index 5: " + str.indexOf("o", 5));

        // lastIndexOf()
        System.out.println("Last index of 'l': " + str.lastIndexOf("l"));

        // equals()
        System.out.println("Equals 'hello wirld!': " + str.equals("hello wirld!"));

        // equalsIgnoreCase()
        System.out.println("Equals Ignore Case: " + str.equalsIgnoreCase(str2));

        // compareTo()
        System.out.println("CompareTo 'hello': " + str.compareTo(str3));

        // compareToIgnoreCase()
        System.out.println("CompareTo Ignore Case: " + str.compareToIgnoreCase(str2));

        // toLowerCase()
        System.out.println("Lowercase: " + str.toLowerCase());

        // toUpperCase()
        System.out.println("Uppercase: " + str.toUpperCase());

        // trim()
        String strWithSpace = "   hello wirld!   ";
        System.out.println("Trim: '" + strWithSpace.trim() + "'");

        // replace()
        System.out.println("Replace 'i' with 'o': " + str.replace('i', 'o'));

        // contains()
        System.out.println("Contains 'wirld': " + str.contains("wirld"));

        // toCharArray()
        char[] arr = str.toCharArray();
        System.out.print("Char Array: ");
        for(char c : arr) {
            System.out.print(c + " ");
        }
        System.out.println();

        // startsWith()
        System.out.println("Starts with 'hello': " + str.startsWith("hello"));
    }
}