[ Java 常見問題 ] How to convert a byte to its binary string representation

Source From Here
Question
I read the byte from a binary file, and stored in the byte array B. I use System.out.println(Integer.toBinaryString(B[i])). the problem is:

(a) when the bits begin with (leftmost) 1, the output is not correct because it converts B[i] to a negative int value.
(b) if the bits begin with 0, the output ignore 0, for example, assume B[0] has 00000001, the output is 1 instead of 00000001

How-To
Use Integer#toBinaryString():

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1. byte b1 = (byte) 129;  
2. String s1 = String.format("%8s", Integer.toBinaryString(b1 & 0xFF)).replace(' ', '0');  
3. System.out.println(s1); // 10000001  
4.   
5. byte b2 = (byte) 2;  
6. String s2 = String.format("%8s", Integer.toBinaryString(b2 & 0xFF)).replace(' ', '0');  
7. System.out.println(s2); // 00000010  

Or you can leverage exist library flib:

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1. package test;  
2.   
3. import flib.util.HexByteKit;  
4.   
5. public class Test {  
6.   
7.     public static void main(String[] args) {  
8.         byte b1[] = {(byte) 129};  
9.         System.out.printf("%s\n", HexByteKit.Byte2Bin(b1));  
10.   
11.         byte b2[] = {(byte) 2};  
12.         System.out.printf("%s\n", HexByteKit.Byte2Bin(b2));               
13.     }  
14. }  

Execution result:

10000001
00000010