BufferedInputStream.read（byte [] b，int off，int len）中的off参数

Question

The javadoc says the following.

Parameters:
    b - destination buffer.
    off - offset at which to start storing bytes.
    len - maximum number of bytes to read.

I would like to confirm my understanding of the "offset at which to start storing bytes". Does this mean that off is "the index at the destination buffer b at which to start storing bytes"? It does sound like off means it. I think the method is more usable if off is the "offset at the BufferedInputStream at which to start reading bytes", but I want to confirm. I tried looking at the source but it's hard to read.

A side question: When 1024 bytes of a stream is read, will the said 1024 bytes always be removed from the stream?

Answer 1

Yes. off is the index in b where the stream will start entering len bytes.

When 1024 bytes of a stream is read, will the said 1024 bytes always be removed from the stream?

Using an InputStream , you have no knowledge of what's going on underneath. All you know are the methods available to you and what they do (what their documentation says). Implementations can do whatever they want.

Answer 2

Does this mean that off is "the index at the destination buffer b at which to start storing bytes"?

It's documented : "The first byte read is stored into element b[off] ".

When 1024 bytes of a stream is read, will the said 1024 bytes always be removed from the stream?

Of course, but you seem to be really asking whether 1024 bytes will always be read if you supply a buffer of 1024 bytes. Answer is no. It's documented : "there is an attempt to read at least one byte".