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Jon Skeet
Java: Why does this string of 4 characters create a byte[] with 6 data?
I need to be able to convert an int into a string which represents a series of bytes, and back. To do this, I came up with this code: Int -> Byte[] -> String
new String(ByteBuffer.allocate(5).putInt(num).array())
String -> Byte[] -> Int
ByteBuffer.allocate(4).put(team.getBytes()).getInt(0)
One of my test cases is the number 4231. When viewed as a string, none of the characters are visible but that's not completely unusual, and when I invoke it's .length() method, it returns 4. But when I used .getBytes(), I get [0, 0, 16, -17, -65, -67], which causes a StackOverflowException. Can someone explain this result to me?
Without knowing the platform default encoding of your machine, it's slightly hard to say - and you should avoid calling String.getBytes without specifying an encoding, IMO.
However, basically a String represents a sequence of characters, encoded as a sequence of UTF-16 code units. Not every character is representable in one byte, in many encodings - and you certainly shouldn't assume it is. (You shouldn't even assume there's one character per char, due surrogate pairs used to represent non-BMP characters.)
Fundamentally, you shouldn't treat a string like this - if you want to encode non-text data in a string, use hex or base64 to encode the binary data, and then decode it appropriately. Otherwise you can easily get invalid strings, and lose data - and more importantly, you're simply not treating the type for the purpose it was designed.
When you convert a byte[] into a String, you're saying "This is the binary representation of some text, in a particular encoding" (either explicitly or using the platform default). That's simply not the case here - there's no text to start with, just a number... the binary data isn't encoded text, it's an encoded integer.
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