Java String to byte conversion issue

Question

I have some test code which is not working as I expect, after reviewing various sites and specifications I still cannot figure out what is happening.

Here is my test code:

byte[] b = new byte[8];
b[0] = (byte)0x72;
b[1] = (byte)0x3A;
b[2] = (byte)0x60;
b[3] = (byte)0x01;
b[4] = (byte)0x0E;
b[5] = (byte)0x10;
b[6] = (byte)0x8A;
b[7] = (byte)0x11;
String bitmapStr = new String(b);
try {
    b = bitmapStr.getBytes("US-ASCII");
} catch (Exception ex) {
    ex.printStackTrace();
}
System.out.println("DEBUG: bitmapStr = \"" +bitmapStr + "\"");
for (int i=0; i<=7; i++) {
    int byte1 = b[i];
    System.out.println("byte"+i + ": " + Integer.toHexString(byte1));
}

When I run the program I get the following in the console output:

DEBUG: bitmapStr = "r:`�"
byte0: 72
byte1: 3a
byte2: 60
byte3: 1
byte4: e
byte5: 10
byte6: 3f
byte7: 11

See how byte6 i.e. b[6] from my byte array outputs 0x3F, but it should be 0x8A.

Any ideas why?

By the way, if I use UTF-8 encoding I get an even more funky output (although ASCII is correct).

UTF-8 String encoding output:

byte0: 72
byte1: 3a
byte2: 60
byte3: 1
byte4: e
byte5: 10
byte6: ffffffef
byte7: ffffffbf

What text character is 0x8A supposed to represent, and in what encoding? It's not ASCII, as previously stated here, and it does not appear to be ISO-8859-1 either. htmlhelp.com/reference/charset/latin1.gif — The111
– The111, Commented Nov 20, 2012 at 7:05

Chris Gerken · Accepted Answer · 2012-11-19 19:59:10Z

5

Try another form of the String constructor:

String bitmapStr = new String(b,"ISO-8859-1");

edited Nov 19, 2012 at 19:59

answered Nov 19, 2012 at 18:00

Chris Gerken

16.4k6 gold badges48 silver badges61 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Steve Over a year ago

This doesn't work - I still get an odd result in byte 6. 8A is of course the only byte value where the most significant bit is set, so I assume the sign is affecting the conversion.

Chris Gerken Over a year ago

Updated my answer per your findings. Thanks.

The111 Over a year ago

No matter what kind of constructor he uses, he is casting a value as a byte which is outside of the byte range. Even if you use the constructor from this answer, you end up with a negative value because of the byte cast.

The111 Over a year ago

Also, I don't think 0x8A is a valid character in ISO-8859-1. htmlhelp.com/reference/charset/latin1.gif

Rahul Tripathi · Accepted Answer · 2012-11-19 18:01:17Z

2

Try something like this to change a string to byte:-

  String source = "2675326";
 byte[] byteArray = source.getBytes("UTF-16LE");

or change your code to:-

 String bitmapStr = new String(b,"US-ASCII");

answered Nov 19, 2012 at 18:01

Rahul Tripathi

173k33 gold badges292 silver badges341 bronze badges

Comments

Alex · Accepted Answer · 2012-11-19 19:15:54Z

1

You are forcing hexadecimal become byte ( 8 bits ). This is called casting and you cannot do that. You notice that all values have a good output except when 0xYZ where Y >=8 ! do not use casting unless you're sure you're not gonna lose information.

answered Nov 19, 2012 at 19:15

Alex

1,6693 gold badges19 silver badges33 bronze badges

1 Comment

Steve Over a year ago

Err, what? Hexadecimal is simply another representation of the data, of course it's valid to cast from hex to byte, they are a different representation of the same thing! When Y>=8 issues occur because ASCII encoding supports up to 7 bits, (the 7th bit is 0x80).

Steve · Accepted Answer · 2012-11-19 18:35:50Z

0

Following the suggestions from Rahul and irreputabe I figured it out:

When I changed to UTF-16LE / ISO-8859-1 encoding, byte6 was output as: "ffffff8a", then I realised I was performing a type conversion from byte to int here:

int byte1 = b[i];

So I just added:

int byte1 = b[i] & 0xFF;

for the correct result.

answered Nov 19, 2012 at 18:35

Steve

3504 silver badges18 bronze badges

Collectives™ on Stack Overflow

Java String to byte conversion issue

4 Answers 4

4 Comments

Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

4 Comments

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related