Question

Part I - Reading input in a loop

Before you start doing any coding, brainstorm between the two of you on how to go about starting this program. You need to get your code to repeatedly prompt for a new String until the user enters an empty line, and then end with a goodbye message. What is the algorithm that you need to use? Write your algorithm into comments in the main method of the Palindrome class (as shown in the class notes). The code you write needs to reproduce the following transcript (user entries are in BOLD):

Enter a string: 1331

Enter a string: racecar

Enter a string: blue

Enter a string:

Empty line read - Goodbye!

Part II - Checking for a palindrome

Now brainstorm with your partner again - once the user has entered a String you need to think about how to tell if it is a palindrome. One way to do this is to compare the characters that are supposed to match - if all of these characters match, then it is a palindrome. If any pair does not match, then it is not a palindrome. Think about the algorithm that does this kind of "pairwise character" comparison - how would you implement that with a loop? Work out the algorithm with your partner and put it into your code, then fill in the code around your algorithm to complete the task. A sample transcript of what your code should do once both parts are completed is below. User entries are shown in BOLD.

Enter a string: 1331

1331 is a palindrome.

Enter a string: racecar

racecar is a palindrome.

Enter a string: blue

blue is NOT a palindrome.

Enter a string:

Empty line read - Goodbye!

Do not worry about differences in case, punctuation, spacing or other issues. Your code should only check whether or not the string of characters is exactly the same forwards as it is backwards.

Enter a string: Racecar

Racecar is NOT a palindrome

Enter a string: RACECAR

RACECAR is a palindrome.

Enter a string: A man, a plan, a canal, Panama.

A man, a plan, a canal, Panama. is NOT a palindrome.

Enter a string: y123321y

y123321y is a palindrome.

Enter a string:

Empty line read - Goodbye!

Use the following template for your code:

public class Palindrome {

public static void main(String[] args) {

// TODO - fill in with your code

}

}

NOTE: You MUST use a nested loop for this assignment. There are other ways to solve this problem, but for this assignment you must have a loop nested inside another loop. Think about using the outer loop to read the String and the inner loop to test for the palindrome.

NOTE 2: For this assignment you need to test whether or not a String is empty (a blank line). Do NOT compare the String with an empty String. Instead, test the length of the String - if it's empty, the length will be 0. You can also use the isEmpty instance method of String if you know how to use it or would like to look it up. Comparing the String with an empty String is less efficient than just checking the length. (Note that to read an empty line on the console, you must use the Scanner's nextLine() method - the next() method skips blank space and so will not read an empty line).

Answer 1

import java.util.Scanner;

public class Palindrome {

public static void main(String[] args) {
  

/*

• While(true):
  • Read input from user
  • If empty string
    • Display mesage
    • Exit While Loop   
  • Else
    • Check if the string is a palindrome or not.
    • Display result

*/

//Scanner variable to get user input
Scanner sc = new Scanner(System.in);
String str;
  
//Loop to get user input
while(true)
{
  
System.out.printf("Enter a string: ");
str=sc.nextLine(); //Getting input from user
  
int slen = str.length(); //Variable to store string length
int flag=0; //Flag variable
  
//If the input is empty
if((slen == 0)){
System.out.println("Empty line read - Goodbye!");
break;
}
else{ //If the user input is not empty
  
//Loop to check if the string is a palindrome or not.
for(int i=0; i<=slen/2 ; i++){
  
//Checking if the character and its counter character from the end are same or not.
if(str.charAt(i)!=str.charAt(slen-1-i))
flag=1; //Flag is set if it is not a palindrome.
}
  
// Printing result
if(flag==0)
System.out.println(str+" is a palindrome.");
else
System.out.println(str+" is NOT a palindrome.");
}
  
  
}
  
}
  
}

Sample Runs: