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Old 03-15-07, 04:23 PM   #1
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Join Date: Mar 2007
Posts: 1
Default Java Help: Palindrome program

Hi, I'm very new to Java programming and I working on a school project. The project is to write a program that scans in a string and determines length, reverses the string and then checks to see if it's a palindrome. Here's the stab I've made so far:

Edit: I found another web site that let me save my reversed info as another separate string. Here is my final code in case anybody wants to looks at it:

import java.util.regex.*;
import java.io.*;
import java.util.Scanner;   // import java.util.Scanner to use the Scanner function

public class cmayproj01
{                           // start class cmayproj01

   public static void main(String[] args)
   {                        // start main
	   print_header();            // call from header

	   System.out.println("Please type a string that contains, at most, 30 characters:");
	   Scanner scanIn = new Scanner(System.in);
	   String strUserInput = scanIn.nextLine();
	   String strInputCopy = strUserInput;


	   String strInputTrimmed = strUserInput.replace(" ", "");

	   System.out.println( "You typed: " + strUserInput);
       System.out.println( "The trimmed version is: " + strInputTrimmed);  // remove from final program
	   System.out.print( "The length is: ");
	   int numberofchars = strInputTrimmed.length();
       System.out.println(numberofchars + " Characters.");

	   reverse(strInputTrimmed, strUserInput);         //called from reverse

	   if (strInputTrimmed.compareTo(strUserInput) == 1)
		   System.out.println( "\nYou didn't type a Palindrome.");	   
		   System.out.println( "\nYou typed a Palindrome!");
   }                    // end main

	                      // start functions
	public static void print_header()
	{                       // start print_header
		System.out.println("This is where the header goes...\n");  // insert header here!!
	}                       // end print_header
    public static void reverse(String strInputTrimmed, String strUserInput)
    {                       // start reverse

		System.out.println("The original string you typed was: " + strUserInput);
		System.out.print("The reverse is: ");

		if (strInputTrimmed.length() == 1)

			int len = strInputTrimmed.length();
			char[] tempCharArray = new char[len];
			char[] charArray = new char[len];

			// put original string in an array of chars
			for (int i = 0; i < len; i++)
				tempCharArray[i] = strInputTrimmed.charAt(i);

			// reverse array of chars
			for (int j = 0; j < len; j++)
				charArray[j] = tempCharArray[len - 1 - j];

			String strInputReverse = new String(charArray);

			if (strInputReverse.compareTo(strInputTrimmed) < 0)
				System.out.println("\nYou didn't type a Palindrome.");
				System.out.println("\nYou typed a Palindrome!");


    }                       // end reverse
}                          // end cmayproj01
I don't feel this is spam but if it is please delete.
DoctorFu is offline   Reply With Quote
Old 03-18-07, 01:14 PM   #2
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Join Date: Sep 2004
Posts: 97
Default Re: Java Help: Palindrome program

have you tested this, because

if (strInputReverse.compareTo(strInputTrimmed) < 0)
System.out.println("\nYou didn't type a Palindrome.");
System.out.println("\nYou typed a Palindrome!");

The compareTo method only does string comparsions lexicographically. This does not ensure that you have a correct palindrome.

I suggest your program for test cases, also your program ignores a string has that spaces, does it handle other characters like ? . , (not sure what the scope of your project is) if it is to handle any kind of string input.
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Cinema4DXL is offline   Reply With Quote
Old 04-24-07, 04:53 PM   #3
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Join Date: Dec 2004
Posts: 933
Default Re: Java Help: Palindrome program

this is quite a bit smaller
// CS161L Wed 3:00 PM
// 9:00 Lecture Mon,Wed,Fri
// Lab9 - lab10.java
import java.util.*;

public class lab10
	public static boolean palindrone(String s, int index)
		if(index == s.length())		// drop out of the loop, string is at the end
			return true;
		char first,last;
		first = s.charAt(index);
		last = s.charAt(s.length()-index-1);
		//System.out.println(first + " " + last);
		if(first == last)
			return palindrone(s,++index);
			return false;
	public static void main(String args[])
		Scanner input = new Scanner(System.in);
		System.out.print("Enter a word, 'quit' to exit: ");
		String in = input.nextLine();
				System.out.println("This is a palindrone");
				System.out.println("This is not a palindrone");
			System.out.print("Enter another word: ");
			in = input.nextLine();
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