Convert byte (java data type) value to bits (a string containing only 8 bits)

Question

I need to convert a value declared as a byte data type into a string of 8 bits. Is there any Java library method that can do this? For example, it should take in -128 and output "10000000". Also, input -3 should give "11111101". (I converted these by hand.)

Before you assume this has been answered many times, please let me explain why I am confused.

The name "byte" is a little ambiguous. So, it's been difficult following other answers. For my question, byte is referring to the java data type that takes up 8 bits and whose value ranges from -128 to 127. I also don't mean an "array of bytes". My question is about converting a single value into its 8-bit representation only. Nothing more.

I've tried these:

byte b = -128;  //i want 10000000
Integer.toBinaryString(b); //prints 11111111111111111111111110000000
Integer.toString(b, 2); //prints -10000000

If there's no built-in method, can you suggest any approach (maybe bit shifting)?

Evgeniy Dorofeev · Accepted Answer · 2013-01-16 17:59:52Z

14

Try

Integer.toBinaryString(b & 0xFF);

this gives a floating length format e.g. 4 -> 100. There seems to be no standard solution to get a fixed length format, that is 4 -> 00000100. Here is a one line custom solution (prepended with 0b)

String s ="0b" + ("0000000" + Integer.toBinaryString(0xFF & b)).replaceAll(".*(.{8})$", "$1");

edited Jan 16, 2013 at 17:59

answered Jan 16, 2013 at 17:22

Evgeniy Dorofeev

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6 Comments

davidXYZ Over a year ago

This seems to work fine. Thanks a lot!! I wonder why they couldn't just have a Byte.toBinaryString method?!?

Evgeniy Dorofeev Over a year ago

I agree. First option I tried (without success) was Byte.toBinaryString.

davidXYZ Over a year ago

I can write a function to ensure the result is padded with zeros up to 8 characters for positive numbers. However, your regex works but I dont understand it. Can u explain?

Evgeniy Dorofeev Over a year ago

I'll try. ".*(.{8})$" means "any text that ends with any 8 chars". (.{8}) - last 8 chars is group #1 (since theres not other group in regex). $1 means "replace with group #1". All in all - take all text and replace it with the last 8 chars. :)

davidXYZ Over a year ago

I do understand now. I've learned something else today. Thanks.

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