Question

I am learning about I/O, Files and Sockets and i don’t understand the meaning of this sentence

read will not always fill a buffer

What does it mean? Anyone has some explanation for me?

Answer 1

The read() method accepts a byte-array that it will fill with from the stream or reader.

If there is not enough data available to fill the buffer, it can either

• wait until enough data is available
• return immediately but only provide the available data without filling the buffer completely.

The standard implementation does a mixtures of both: It waits until at least one byte is available.

Note: The second case implies that read() may return without any data at all.