Comparison for Strings constructed with uninitialized byte array cells

Question

A follow up to one I asked long time ago, I'm trying to construct Strings from byte arrays which may not have all cells set to a specific value (cf. code below). It seems that if a String is constructed from suchlike byte array, the allocated-but-unset bytes still counts, making comparisons (using equals()) fail.

See,

public class Test{
    public static void main(String[] args){
        byte[] b = new byte[10];
        String s = "RESET ME";
        for(int i = 0; i < 8; i++){
            b[i] = (byte) s.charAt(i);
        }
        String s2 = new String(b);
        System.out.println(s.equals(s2));
    }
}

Which prints "false". Short of writing my own comparator, is there a way to compare Strings such that it does not take the unset bytes into account?

"uninitialized" byte[] cells will be 0 (so the corresponding characters in the String will be U+0000). This is not undefined behaviour in Java. — Joachim Sauer
– Joachim Sauer, Commented Jul 16, 2013 at 11:53
And as a general note: why do you have characters in your String that you do not care about in the first place? Get rid of those, and continue working with a sane String. — Joachim Sauer
– Joachim Sauer, Commented Jul 16, 2013 at 11:54
That came from a buffer data structure I was using. Basically, I was listening for transactions over a socket, but it may happen that the transaction terminates without using everything in the buffer, hence the blank cells. — skytreader
– skytreader, Commented Jul 17, 2013 at 1:59

hmjd · Accepted Answer · 2013-07-16 11:18:04Z

2

Why not keep it simple and construct the string built from the byte[] using the String(bytes, offset, len) constructor and avoid including the unset bytes at all:

String s2 = new String(b, 0, 8);

edited Jul 16, 2013 at 11:18

answered Jul 16, 2013 at 11:12

hmjd

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