从类Reader读取（char [] cbuf，int off，int len）

Question

To my understanding, this abstract method reads characters into a portion of an array.

What confuses me is that it returns the number of character read, or -1 if it reaches the end of stream.

Does that mean that the read method read 1 character at a time and return the no. of character read, and then once it hits the end it returns -1?

Eg, if it's reading a string "abcd" form a txt file with read(cbuf, 0 4), it returns 1234 and finally -1?

And if that's the case, does that mean we can only access the read characters through cbuf?

edit2: Thanks again everyone, I finally figured out everything. Cheers!

Answer 1

In general, the read method (from various classes) will read up to a maximum of len characters in one operation. It might read fewer characters. You should check the return value of the function to know how many such characters it read.

Once it reaches the EOF, it will return -1.

Answer 2

Take a look at the Documentation of BufferedReader.read :

This method implements the general contract of the corresponding read method of the Reader class. As an additional convenience, it attempts to read as many characters as possible by repeatedly invoking the read method of the underlying stream. This iterated read continues until one of the following conditions becomes true:

1. The specified number of characters have been read
2. The read method of the underlying stream returns -1, indicating end-of-file.
3. The ready method of the underlying stream returns false, indicating that further input requests would block.

...

If the first read on the underlying stream returns -1 to indicate end-of-file then this method returns -1. Otherwise this method returns the number of characters actually read.

....

Ordinarily this method takes characters from this stream's character buffer, filling it from the underlying stream as necessary. If, however, the buffer is empty, the mark is not valid, and the requested length is at least as large as the buffer, then this method will read characters directly from the underlying stream into the given array.