InputStream in = new FileInputStream(file);int q;while ((q = in.read()) != -1) { ...}
The code above reads a file byte by byte. Every read() method call on the stream causes a native call to native implementation of the filesystem. Depending on the implementation this may cause a syscall to the operating system. The number of native calls can be reduced significantly by wrapping the stream into a BufferedInputStream:
InputStream in = new BufferedInputStream(new FileInputStream(file));