Echo.java

import java.util.Scanner;

public class Echo{
    public static void main(String[] args) {
        // Create a Scanner object to read user input
        Scanner scanner = new Scanner(System.in);

        // Prompt the user for input
        System.out.print("Enter a string (at least three characters long): ");
        String userInput = scanner.nextLine();

        // Close the scanner to free up resources
        scanner.close();

        // Check if the input is at least three characters long and the last three characters are letters
        if (userInput.length() < 3 || !areLastThreeCharactersLetters(userInput)) {
            System.out.println("Invalid input. Please enter a string of at least three characters with letters at the end.");
            System.exit(0);; // Terminate the program
        }

        // Line 1: Repeat the entire input in uppercase letters (initial amplification)
        System.out.println(userInput.toUpperCase());

        // Line 2: Repeat the last three characters in uppercase letters
        System.out.println(userInput.substring(userInput.length() - 3).toUpperCase());

        // Line 3: Repeat the last three characters in lowercase letters
        System.out.println(userInput.substring(userInput.length() - 3).toLowerCase());

        // Line 4: Repeat the last two characters in lowercase letters
        System.out.println(userInput.substring(userInput.length() - 2).toLowerCase());

        // Line 5: Repeat the last character in lowercase letters
        System.out.println(userInput.charAt(userInput.length() - 1));
    }

    // Method to check if the last three characters of a string are letters
    public static boolean areLastThreeCharactersLetters(String str) {
       // check if str is null

       
        int length = str.length();
        if (length < 3) {
            return false;
        }
       // boolean allLetters = str.chars().allMatch(Character::isLetter);
        char char1 = str.charAt(length - 3);
        char char2 = str.charAt(length - 2);
        char char3 = str.charAt(length - 1);

        return Character.isLetter(char1) && Character.isLetter(char2) && Character.isLetter(char3);
    }


    // public static boolean areLastThreeCharactersLetters(String str) {
    //     int length = str.length();
    //     if (length < 3) {
    //         return false;
    //     }
    //     String lastThree = str.substring(str.length()-3 );
    //     boolean allLetters = str.substring(str.length()-3 ).chars().allMatch(Character::isLetter);
    //     //
    //     return allLetters;
    // }
}