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I'm having some trouble with a question from my programming II class and have hit a brick wall, was wondering if someone could help?
The question asks for a user to input a string, the program to reverse the input string and then to compare the reverse to the original, this must be done recursively.
So far I have:
public class question1
{
public static void main(String args[])
{
String input = JOptionPane.showInputDialog(null, "Please enter a sentence to determine if it is a palindrome.");
String backwardsinput = Reverse(input);
System.out.println(backwardsinput);
boolean Palindrome = PalindromeCheck(backwardsinput, input);
if (Palindrome == true)
{
JOptionPane.showMessageDialog(null,"That is a palindrome!");
}
if (Palindrome == false)
{
JOptionPane.showMessageDialog(null,"That is not a palindrome");
}
}
public static String Reverse (String input)
{
if (input.length() <= 1)
return input;
else
{
char x = input.charAt(input.length()-1);
return x+Reverse(input.substring(0,input.length()-1));
}
}
public static boolean PalindromeCheck (String backwardsinput, String input)
{
if(input.length() == 0 || input.length() == 1)
return true;
if(backwardsinput.charAt(0) == input.charAt(input.length()-1))
return PalindromeCheck(backwardsinput.substring(1, backwardsinput.length()-1), input.substring(1, input.length()-1));
else
return false;
}
}
My problem is, it tells me everything is a palindrome, I've looked at it over and over and can't figure out why!
738
String strcmp() function in C++ In order to compare two strings, we can use String's strcmp() function. The strcmp() function is a C library function used to compare two strings in a lexicographical manner. The function returns 0 if both the strings are equal or the same.
You should not use == (equality operator) to compare these strings because they compare the reference of the string, i.e. whether they are the same object or not. On the other hand, equals() method compares whether the value of the strings is equal, and not the object itself.
String Comparison With Objects Class The method returns true if two Strings are equal by first comparing them using their address i.e “==”. Consequently, if both arguments are null, it returns true and if exactly one argument is null, it returns false.
Java String compareTo() MethodThe method returns 0 if the string is equal to the other string. A value less than 0 is returned if the string is less than the other string (less characters) and a value greater than 0 if the string is greater than the other string (more characters).
You're doing the work twice (sort of).
if(backwardsinput.charAt(0) == input.charAt(input.length()-1))
^^^^^^^^^^^^^^^^
should be
if (backwardsinput.charAt(0) == input.charAt(0))
^
You almost got it :-)
Also, another way of expressing
if (cond)
return something;
else
return false;
is
return cond && something;
thus your last lines could be written as
return backwardsinput.charAt(0) == input.charAt(0) &&
palindromeCheck(backwardsinput.substring(1, backwardsinput.length() - 1),
input.substring(1, input.length() - 1));
Related question / answer:
118
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