How to convert efficiently binary string to binary byte array in Java?

Question

As an input I have binary string String a = "100110". As output I need to have binary byte array byte[] b = {1,0,0,1,1,0}. For now I'm using

for (int i=0; i<a.length; i++) { b[i]= Byte.parseByte(a.substring(i, i+1)); }

But this approach is too slow. Can any one give a better suggestion? Thank you

possible duplicate of [Store binary sequence in byte array?](http://stackoverflow.com/questions/5409998/store-binary-sequence-in-byte-array) — Nivas, Jun 24 '14 at 20:50
@Nivas I don't think it's a duplicate, because it looks like OP wants to split each bit in its own byte. — Sergey Kalinichenko, Jun 24 '14 at 20:52
http://stackoverflow.com/questions/17727310/convert-binary-string-to-byte-array — jlars62, Jun 24 '14 at 20:54

score 6 · Accepted Answer · answered Jun 24 '14 at 20:51

You can do it without making objects for substrings, like this:

for (int i=0; i<a.length; i++) {
    b[i]= a.charAt(i)=='1' ? (byte)1 : (byte)0;
}

The reason your approach is slower is that each call to substring produces a new String object, which becomes eligible for garbage collection as soon as parseByte is done with it.

score 5 · Answer 2 · answered Jun 24 '14 at 20:56

5

Assuming the input is valid...

    byte[] b = new byte[a.length()];
    for (int i = 0; i < b.length; i++) {
        b[i] = (byte) (a.charAt(i) - '0');
    }

answered Jun 24 '14 at 20:56

roozbeh

809
7
4

score 1 · Answer 3 · answered Jun 24 '14 at 21:58

Makes an int[] instead of byte[] but I hope for points for elegance:

    int[] a = "100110"
            // Turn it into a stream.
            .chars()
            // Make '0'/'1' into 0/1
            .map(c -> c - '0')
            // Roll it into an array.
            .toArray();

How to convert efficiently binary string to binary byte array in Java?

3 Answers3

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