Question

The FileInputStream read method has the signature (is that the right term?) –

     public int read(byte[] b) throws IOException

     // Reads up to b.length bytes of data from this input stream into an array of bytes. This method blocks until some input is available.
     // Returns: the total number of bytes read into the buffer, or -1 if there is no more data because the end of the file has been reached.

What is the advantage of having a signature like this over something like this –

     public byte[] read(int numberOfBytes) throws IOException
     // Reads up to numberOfBytes bytes of data from this input stream into an array of bytes.
     // Returns- an array of bytes read. Array is empty if there is no more data because the end of the file has been reached.

Answer 1

The first form allows you to reuse the same byte[] array for several executions. Basically you can read the whole stream producing minimal garbage (low GC activity).

The latter is clearly more convenient but requires creating new instance of byte[] every time it is executed internally within read() method. This means that while reading 10 GiB file (even in 100-byte chunk) your application would allocate 10 GiB of memory in total – not at the same time, but still the garbage collector would work like crazy.

Have a look at Collection.toArray(T[]) – it follows the same principle.