Java performance of byte[] vs. char[] for file stream

Question

I'm writing a program that reads a file (uses custom buffer, 8KB), then finds a keyword in that buffer. Since Java provides two type of streams: character & byte, I've implemented this using both byte[] and char[] for buffering.

I just wonder, which would be faster and better for performance, since a char is 2 byte and when using Reader to read up char[] , the Reader will perform converting back from byte to char , which I think could make it slower than using only byte[] .

Answer 1

Using a byte array will be faster:

• You don't have the bytes to characters decoding step, which is at least a copy loop, and possibly more depending on the Charset used to do the decoding.

• The byte array will take less space, and hence save CPU cycles in GC / initialization.

However:

• Unless you are searching huge files, the difference is unlikely to be significant.

• The byte array approach could FAIL if the input file is not encoded in an 8 bit character set. And even if it works (as it does for UTF-8 & UTF-16) there are potential issues with matching characters that span buffer boundaries.

(The reason that byte-wise treatment works for UTF-8 and UTF-16 is that the encoding makes it easy to distinguish between the first unit (byte or short) and subsequent units of an encoded character.)

Answer 2

If it's a binary file you're reading use a byte array.

If it's a text file and you're going to be using the contents like strings later then you should use a char array.

Answer 3

This stack overflow question file-streaming-in-java talks about streaming files efficiently in java.

I particularly likethis reference article

On large files, you quickly have advantages of speed using only bytes, so if you can decode the pattern through bytes you could definitively gain a few precious cycles.

If your files are small, or you don't have so many, maybe it's not worth the trouble.