converting a hex string back to a string, in Java

Question

I am struggling trying to convert a hex number string back to the original string. I convert the string using the following method:

 private static String hex(String  binStr) {

        String newStr = new String();

        try {
            String hexStr = "0123456789ABCDEF";
            byte [] p = binStr.getBytes();
            for(int k=0; k < p.length; k++ ){
                int j = ( p[k] >> 4 )&0xF;
                newStr = newStr + hexStr.charAt( j );
                j = p[k]&0xF;
                newStr = newStr + hexStr.charAt( j ) + " ";
            }   
        } catch (Exception e) {
            System.out.println("Failed to convert into hex values: " + e);
        } 

        return newStr;
    }

I am really stuck, and any advice would be greatly appreciated.

Thank you in advance

Could you give sample input and the expected output?

Louis Wasserman
– Louis Wasserman

2012-11-18 17:48:05 +00:00
Commented Nov 18, 2012 at 17:48 — Louis Wasserman
– Louis Wasserman, Commented Nov 18, 2012 at 17:48

Evgeniy Dorofeev · Accepted Answer · 2012-11-18 17:55:22Z

1

Consider this:

     String hexStr = "0123456789ABCDEF";
     long i = Long.valueOf(hexStr, 16);
     System.out.println(Long.toHexString(i));

answered Nov 18, 2012 at 17:55

Evgeniy Dorofeev

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Comments

Patricia Shanahan · Accepted Answer · 2012-11-18 17:55:47Z

1

The code in the question destroys information. Only the most significant two bits and the least significant four bits of each input byte contribute to the result. That means it cannot, in general, be reversed.

If the right shift had been by four bits, instead of 6:

int j = ( p[k] >> 4 )&0xF;

all the input would have been preserved, and the original string could have been recovered from the hex string. Maybe you really meant the four bit shift?

answered Nov 18, 2012 at 17:55

Patricia Shanahan

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2 Comments

Pectus Excavatum Over a year ago

Yes sorry, I did indeed mean 4 bits; >> 4

Patricia Shanahan Over a year ago

Which version did you actually use to generate the string you are trying to convert back?

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