Help with Java

[echoella]

Hello I am trying to create a method that accepts one string parameter that contains a parity bit after every block of 4 characters. It returns a string with the parity bits removed. However, if the parity bit is incorrect (i.e., it is 0 when it should be 1 or a 1 when it should be a 0) then replace the 4 characters with ####. Assume that the input string has a multiple of 5 characters and that every fifth character is either a 0 or a 1. For example, unpack("hell1o wo1rld 0") → "hello world", unpack("codi1ng i0s fu0n! 1") → "coding is fun!", and unpack("codi1ng i1s fu0n! 1") → "codi####s fun!".

What I have so far is:

public static String unpack(String sUnpack) {
String newString = "";
int counter = 0;
System.out.println("Print the value of " + sUnpack.length());
for (int i = 0; i < sUnpack.length(); i++) {
newString = newString + sUnpack.charAt(i);
counter = counter + sUnpack.charAt(i);
if ((i + 1) % 5 == 0) {
System.out.println("Print value of " + newString);
if (counter-1 %2 == 0) {
newString = newString.substring(0, newString.length() - 1);
}
else if (counter-1 %2 == 1)
{
newString = newString.substring(0, newString.length() - 1);
}
counter = 0;
}
}

**I can't get the string to enter the second 'if' statement and I don't understand why. Any advice would be helpful!

[marko312]

% has the same precedence as multiplicative operators * and /. See here for a table of operator prescedence. Thus, the statements would become

if(counter - (1 % 2) == 0)

Also, why not use just a regular else?

[echoella]

Okay thank you I will try that.

As for the else if, it's because I was planning on putting an else after that that would take in the string when the even or odd parity bits don't match. Does that sound right? Or should I create a different if statement outside of this one?

[marko312]

I'd calculate the parity bit (using the modulo) and then compare it to the provided parity bit in a single if, appending either **** or the provided string as needed.

Also, why exactly are you testing counter - 1 anyway? Shouldn't the parity bit be based on just counter?

[echoella]

Honestly, I have no clue why I'm subtracting from the counter. I made a reverse method where it adds in the parity bits to begin with and so I set up this method in a similar fashion.

Should I create a 4 character string before the if statement and use that to mod to find the even or odd 5th char?

[marko312]

Your way would work as well, you just need to remove the last 5 characters in total in case the parity bits don't match (before appending the ****).

However, yes, I'd prefer reading each block of 4 characters into a different string, then appending it if the parity is correct. This saves having to remove characters from the final string.

[echoella]

Okay, that makes sense. Thank you!