I have a string of ones and zeros that I want to convert to an array of bytes.
For example String b = "0110100001101001" How can I convert this to a byte[] of length 2?
3 Answers
Parse it to an integer in base 2, then convert to a byte array. In fact, since you've got 16 bits it's time to break out the rarely used short.
short a = Short.parseShort(b, 2);
ByteBuffer bytes = ByteBuffer.allocate(2).putShort(a);
byte[] array = bytes.array();
6 Comments
Luiggi Mendoza
What if the String contains too many bits that it can't be hold even in a
long variable?
Jeff Foster
If the string is too big, then you'll get a
NumberFormatException. I'm making assumptions that it's less than 32 characters for this small example.Luiggi Mendoza
Then this is not a bullet-proof solution. Is there any with simple code or it involves manual working on the String contents?
Jeff Foster
I'm not sure this could get much simple? If
b is in an invalid format a NumberFormatException will be thrown and it's up to the callee to handle the error. Open to suggestions on how to improve this, but I think this is enough of an answer to illustrate the point.
Steve P.
@LuiggiMendoza using
BigInteger as the other answer suggested will take care of that issue. |
Another simple approach is:
String b = "0110100001101001";
byte[] bval = new BigInteger(b, 2).toByteArray();
4 Comments
Evgeniy Dorofeev
it cannot parse "1110100001101001"
will
See stackoverflow.com/questions/24158629/… You might have some sign issues.
Line
When I'm displaying byte[] fspec = new BigInteger("10000000", 2).toByteArray();, it shows [B@3b22cdd0 instead of expected value - why?
Andreas
@Line Because you're displaying it wrong. See What's the simplest way to print a Java array?
Assuming that your binary String can be divided by 8 without getting a rest you can use following method:
/**
* Get an byte array by binary string
* @param binaryString the string representing a byte
* @return an byte array
*/
public static byte[] getByteByString(String binaryString){
Iterable iterable = Splitter.fixedLength(8).split(binaryString);
byte[] ret = new byte[Iterables.size(iterable) ];
Iterator iterator = iterable.iterator();
int i = 0;
while (iterator.hasNext()) {
Integer byteAsInt = Integer.parseInt(iterator.next().toString(), 2);
ret[i] = byteAsInt.byteValue();
i++;
}
return ret;
}
Don't forget to add the guava lib to your dependecies.
In Android you should add to app gradle:
compile group: 'com.google.guava', name: 'guava', version: '19.0'
And add this into project gradle:
allprojects {
repositories {
mavenCentral()
}
}
Update 1
This post contains a solution without using Guava Lib.
104in position 0, and105in position 1?