Java I/O

I/O in General

Input and output in Java is complicated, but then it is in many programming languages. As far as this topic is concerned, I/O refers to bytes that are input or output from devices such as the keyboard, the console, files on disk, webpages, etc. We are not using I/O to refer to events that happen in a GUI environment (mouse clicks, mouse movements, typing into a textbox, etc.).

There are at least three different ways of dealing with I/O.

Character based. C does this with commands like c = getch(); which gets one character from the keyboard. Java does not do single character based I/O. You cannot enter a single character; you always have to press "Enter" as well. (Swing graphics will detect keypresses through event listeners.)
Streams. All Java I/O is based on a stream of characters either coming into the program or going out of the program. It doesn't really matter where the stream goes or what is in it, it is treated the same way.
Note:There is a Stream class which deals with processing objects. This is NOT the same type of stream as I/O streams.
Blocks. There is a Java package called java.nio which
"provides high-speed, block-oriented I/O in standard Java code. By defining classes to hold data, and by processing that data in blocks, NIO takes advantage of low-level optimizations in a way that the original I/O package could not, without using native code."
We won't be looking at this, as it is only for quite advanced and very large applications.
Java nio is also used if you need to work with file attibutes and timestamps.
(To find out more information Google "java nio tutorial" or read http://www.cs.brown.edu/courses/cs161/papers/j-nio-ltr.pdf)

Java I/O - Streams

All of the (stream) classes involved in Java I/O are in the package java.io.* so this must be imported at the beginning of your program.

There are two main types of streams / data:

characters: these are simple ASCII and UniCode characters like what you are reading right now.
binary: this is data that is encoded as bytes / binary. It can't be read unless you know what you are looking for and how it was stored.

For example, this is the first part of a PNG file:

<89>PNG^M ^Z ^@^@^@^MIHDR^@^@^Fr^@^@^Dø^H^B^@^@^@£nËÄ^@^@^@^CsBIT^H^H^HÛáOà^@^@ ^@IDATx<9c>ì½[¬$YvÖ^_×¼g<9e><93>'Ï¥NUwOwÑ=^^^O3Ã<8c>Ç3ú^K<8c>^Q ^^<90>A^H<81><85>,<81>xàÑ^Rh^P<96><90>ü<80><84><90>^X!xC¼ò<80>ÄE .ób^KÉFB6XØô^L<92>/Í´§«»ª»ªÎ5O^ã^^ñ^?ø¦·<82>ÈÌÈÈÌ<88>È<88>Èï÷P:çTfäÎ}Y{o¯½·ü<8d>o|ãïý½¿÷^Wÿâ_ìv»R^F^DA Ëòvïõ}_Q<94>T<8a>±öQ¦iÖj5×ukµZä¿^\ÇÑu=<95>bÄc^XF³Ù<

and here is the first part of an MP3 file:

D3^C^@^@^@^@^FTENC^@^@^@^A@^@^@WXXX^@^@^@^B^@^@^@^@TCOP^@^@^@^A^@^@^@TYER^@^@^@^A^@^@^@My PrayerTALB^@^@^@^A^@^@^@COMM ^@^@^@^X^@^@^@eng^@with Andrea BocelliTCON^@^@^@^A^@^@^@ TRCK^@^@^@^A^@^@^@TSSE^@^@4%Órù^?ÿósKPoÿüÞ¢ù}6OÿÿúÓu <81>»<97>?ÿùpÂ<83>^GÖ^_<80>^@^PbZåM<92>±^S^Uô<84>µI<9a>~1Ê²íÁØWÿû<92>d^L^Dc*MÙ¿a^@^@;¢ªÜæ ^@^Mi=aL<«É^M^K+(ö à<y%<85>^@<91>Ç2Ô¥Gõ4´ì{^^ÕÒýè3G^Zc©µ^M^QwÄ}Wë2ª´·ßÿÿ^MñÜ^?èË^EÉ0i£<95>Ùçêa¢âïº<84>

We'll be focusing on character streams and only look at binary streams if we have time.

Java IO classes appear complicated ...