Question

I have a string that I am creating, and I need to add multiple “\0” (null) characters to the string. Between each null character, is other text data (Just ASCII alphanumeric characters).

My problem is that in J2SE when you add the first null (\0), java then seems to determine that it’s a string terminator, (similar to C++), and ignores all other data being appended. No error is raised, the trailing data is just ignored. I need to force the additional trailing data after a null in the string. I have to do this for a legacy database that I am supporting.

I have tried to encode/decode the string in hoping that something like %00 would fool the interpretation of the string behaviour, but when I re-encode the string, Java sees the null character again, and removes all data after the first null.

Update: Here is the relevant code snippet. Yes, I am trying to use Strings. I intend to try chars, but I still have to save it into the database as a string, so I suspect that I will end up with the same problem.

Some background. I am receiving data via HTTP post that has “\n”. I need to remove the newlines and replace them with “\0”. The “debug” method is just a simple method that does System.out.println.

                String[] arrLines = sValue.split("\n");
                for(int k=0;k<arrLines.length;k++) {
                    if (0<k) {
                        sNewValue += "\0";
                    }
                    sNewValue+= arrLines[k];
                    debug("New value =" + sNewValue);
                }

sNewValue, a String, is committed to the database and needs to be done as a String. What I am observing when i display the current value of sNewValue after each iteration in the console is something like this:

input is value1\nValue2\nValue3
Output in the console is giving me from this code

value1
value1
value1

I am expecting

value1
value1 value2
value1 value2 value3 

with non-printable null between value1, value2 and value3 respectively. Note that the value actually getting saved back into the database is also just “value1”. So, it’s not just a console display problem. The data after \0 is getting ignored.

Answer 1

I strongly suspect this is nothing to do with the text in the string itself – I suspect it’s just how it’s being displayed. For example, try this:

public class Test {
    public static void main(String[] args) {
        String first = "first";
        String second = "second";
        String third = "third";
        String text = first + "\0" + second + "\0" + third;
        System.out.println(text.length()); // Prints 18
    }
}

This prints 18, showing that all the characters are present. However, if you try to display text in a UI label, I wouldn’t be surprised to see only first. (The same may be true in fairly weak debuggers.)

Likewise you should be able to use:

 char c = text.charAt(7);

And now c should be 'e' which is the second letter of “second”.

Basically, I’d expect the core of Java not to care at all about the fact that it contains U+0000. It’s just another character as far as Java is concerned. It’s only at boundaries with native code (e.g. display) that it’s likely to cause a problem.

If this doesn’t help, please explain exactly what you’ve observed – what it is that makes you think the rest of the data isn’t being appended.

EDIT: Another diagnostic approach is to print out the Unicode value of each character in the string:

for (int i = 0; i < text.length(); i++) {
    System.out.println((int) text.charAt(i));
}