In Java, InputStream and OutputStream deal with byte[], and Reader and Writer with char[].
Do their input or output byte[] and char[] essentially have the same values? (That is my impression, because a char and a byte in IO have the same value)
In other words, are InputStream and Reader essentially the same, and are OutputStream and Writer essentially the same?
They're not essentially the same, but they do the same sorts of things for different kinds of data.
InputStream and OutputStream work in bytes. You'd use them when dealing with non-textual information (such as an image).
Reader and Writer work in characters. You'd use them when dealing with textual information.
So "yes" and "no". :-) InputStream and Reader are both for reading information (a stream of bytes or a stream of characters, respectively), and OutputStream and Writer are both for writing information (a stream of bytes or a stream of characters, respectively). Which you use depends on what kind of data you're dealing with. The streams are byte-oriented. The readers/writers are character-oriented.
There are bridging classes between the two kinds of data:
InputStreamReader reads from an InputStream and converts bytes to characters using a CharSet (one provided explicitly or by name).OutputStreamWriter does the converse: Converts characters to bytes (again via a CharSet) and writes the bytes to an OutputStream....but most Reader/Writer subclasses read from/write to sources/destinations that are already character-based, and so don't deal with bytes at all. For instance, StringReader reads characters from a string. Since the source (the string) is already character-based, the Reader doesn't ever deal with bytes, just characters.