[ Java 常見問題 ] Convert hex string to binary string

Source From Here
Question
I would like to convert a hex string to a binary string. For example, Hex 2 is 0010. Below is the code:

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1. String HexToBinary(String Hex)  
2. {  
3.     int i = Integer.parseInt(Hex);  
4.     String Bin = Integer.toBinaryString(i);  
5.     return Bin;  
6. }  

However this only works for Hex 0 - 9; it won't work for Hex A - F because it uses int. Can anyone enhance it?

How-To
You need to tell Java that the int is in hex, like this:

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1. String hexToBinary(String hex) {  
2.     int i = Integer.parseInt(hex, 16);  
3.     String bin = Integer.toBinaryString(i);  
4.     return bin;  
5. }  

Another approach is to used exist library. For example, 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.         String hexStrs[] = { "12F", "3E" };       
9.         try {  
10.             for (int i = 0; i < hexStrs.length; i++) {  
11.   
12.                 String hxs = hexStrs[i];  
13.                 String obs = HexByteKit.Hex2Bin(hxs);  
14.                 System.out.printf("%s(%d)=%s\n", hxs,  
15.                         Integer.parseInt(hxs, 16), obs);  
16.             }  
17.         } catch (Exception e) {  
18.             e.printStackTrace();  
19.         }  
20.     }  
21. }  

Execution result:

12F(303)=000100101111
3E(62)=00111110