testing palindromes with nested loops ONLY

Question

I need to write a program that gets a string from the user and tests to see if it's a palindrome. This has to be done with nested loops: I can't write a method to return the answer. I also have to keep accepting string inputs and testing them until the user enters an empty line, at which point the program prints 'goodbye' and terminates. What I'm having trouble with is getting the program to accept input after the two possible points of input (is a palindrome, is not), and to then use the new input in the loops, and print the appropriate line each time.

Here's what the output is supposed to look like:

Enter a string: rotor

rotor is a palindrome.

Enter a string: mummy

mummy is not a palindrome.

Enter a string:

Empty line read. Goodbye.

This is what I have so far, and it tests each input and returns the correct statement, but it does nothing when the input is empty:

System.out.print("Enter a string: ");
String input = in.next();
if (input.length() > 0) {
     int x = 0;
     int y = input.length()-1;
     while (x < y) {
          if (input.charAt(x) == input.charAt(y)) {
               x++;
               y--;
          }
          else {
               System.out.println(input + " is NOT a palindrome.");
               System.out.println("Enter a string: ");
               input = in.next();
          }
          System.out.println(input + " is a palindrome.");
          System.out.println("Enter a string: ");
          input = in.next();
     }
}
else {
     System.out.print("Empty line read - Goodbye!");
}

Any thoughts? This is homework, btw, so I'm not looking for The Answer so much as clues, or what I need to be looking at.

*"I can't write a method to return the answer"* - You can and should. Putting all of the code into the `main` function isn't very good design. Just because you're using loops doesn't mean you can't move each level of abstraction to its own function. The "game loop" (requesting input over and over) might be in `main`, but when input is received it should be passed to a function. That function may contain a loop, though the contents of that loop may also make sense as being a function. Any small single element of logic should be in its own function. — David, Oct 02 '12 at 21:09

Rohit Jain · Accepted Answer · 2012-10-02T21:11:57.677

2

OK, Since it's your homework, I'll just give you a brief description about how you can proceed: -

Since you need to continously take user input, so probably you would be needing some kind of loop, that can continue until a condition is reached (You can think, what loop constrct will go here)
Secondly, you need to ask user when he want to quit, so you need to specify a exit condition..
Third, for checking for palindrome, you need to check a string with it's reverse..
Since you have to use nested loop, you can use length of the string entered, in your loop condition.. Remember, you just need to loop till half the length. Why, you need to find out.. then, compare first character with last, then 2nd character with 2nd last.. until characters are matching.. You need to find out when you will exit the loop..

I think this much information will get you started..

Also one more thing.. May be you are restricted with the use of any method, but it is absolutely bad idea and ugly design to do everything in main().. In fact any of your method should not do more than one task.. And especially your main() method should ideally be just 4 - 5 lines long..

When coding a method, if you think this part is something different, move it outside to another method, and invoke it.. This is the way you should code..

edited Oct 02 '12 at 21:11

answered Oct 02 '12 at 21:06

Rohit Jain

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Added the code I've got so far to the question. My problem seems to be getting the program to print out the 'goodbye' bit when the input is an empty string. – mattjulian Oct 02 '12 at 21:52
@mattjulian.. This may be because, your empty string contains a newline.. Try `input.replaceAll("(\\r|\\n)", "").length() > 0` in your if.. – Rohit Jain Oct 03 '12 at 04:23
@mattjulian. Or you can try `input.trim().length() > 0` – Rohit Jain Oct 03 '12 at 04:29
thx, i figured it out. had to change it to `in.nextLine()`. and then i moved everything inside a `while` loop that tested for a palindrome until an empty line was input. – mattjulian Oct 03 '12 at 04:41
Yup.. you got it right.. you should use `nextLine` if you don't want your ending newline to be added to your input.. good :) – Rohit Jain Oct 03 '12 at 04:55

testing palindromes with nested loops ONLY

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