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Question

Could someone please point out the mistake in my program?

The output is always: "it is not a palindrome"

String newstr="";
for(int j=length-1;j>0;j--)
{
    char m=str.charAt(j);
    newstr=newstr+m;
}
if(newstr.equals(str) )
    System.out.println("it is a palindrome");
else
    System.out.println("it is not a palindrome");

thanks in advance:)

Answer 1

First of all, use String.equals() to compare Strings instead of == .

if(newstr.equals(str))

Also, string index start with 0, so you need:

for(int j=length-1;j>=0;j--)

Both fixes should work.

Answer 2

if(newstr==str)

should probably be

if ( newstr.equals( str ) )

And do read up on object comparison. You're effectively comparing two pointers, not the string contents.

Of course, with Java 5 and onwards you could just do

new StringBuilder( str ).reverse().toString().equals( str );

Cheers,

Answer 3

index of array starts from 0. I guess you should use

for(int j=length-1;j>=0;j--)

instead of

for(int j=length-1;j>0;j--)

Answer 4

== operator check whether both the reference point to the same object or not. .equals() method will actually check the content of the Strings.

So your code must be

    if(newstr.equals(str))
    System.out.println("it is a palindrome");
    else
    System.out.println("it is not a palindrome");

Answer 5

== tests for reference equality.

.equals() tests for value equality.

Consequently, if you actually want to test whether two strings have the same value you should use .equals() (except in a few situations where you can guarantee that two strings with the same value will be represented by the same object

This will be the final code. read about string comparison in java

  String newstr="";

   for(int j=length-1;j>0;j--)
   {
       char m=str.charAt(j);
       newstr=newstr+m;
    }
    if(newstr.equals( str ) )
    System.out.println("it is a palindrome");
    else
    System.out.println("it is not a palindrome");

Answer 6

public static boolean isPaliandrome(String str) {
        StringBuilder lettersBuff = new StringBuilder(str);
        String str_inverse = lettersBuff.reverse().toString();
        char[] charArrayInverse = str_inverse.toCharArray();
        boolean isPaliandrome = false;
        String caracInverseConverted = new String(charArrayInverse);
        if (str.equals(caracInverseConverted)) {
            isPaliandrome = true;
        }
        return isPaliandrome;
    }