Java I/O – The Basics

JAVA I/O – THE BASICS

•         Java I/O is based around the concept of a stream

–   Ordered sequence of information (bytes) coming from a source, or going to a

‘sink’

–   Simplest stream reads/writes only a single byte, or an array of bytes at a time

•         Designed to be platform-independent

•         The stream concept is very generic

–   Can be applied to many different types of I/O

–   Files, Network, Memory, Processes, etc

•         The java.io package contains all of the I/O classes.

–   Many classes specialised for particular kinds of stream operations, e.g. file I/O

•         Reading/writing single bytes is quite limited

–   So, it includes classes which provide extra functionality

–   e.g. buffering, reading numbers and Strings (not bytes), etc.

•         Results in large inheritance hierarchy, with separate trees for input and output stream classes

Java I/O – InputStream

Java I/O – InputStreams

•         I/O in Java:

InputStream in = new FileInputStream(“c:\\temp\\myfile.txt”); int b = in.read();

//EOF is signalled by read() returning -1 while (b != -1)

{

//do something… b = in.read();

}

in.close();

• But using buffering is more efficient, therefore we always nest our streams… InputStream inner = new FileInputStream(“c:\\temp\\myfile.txt”);

InputStream in = new BufferedInputStream(inner); int b = in.read();

//EOF is signalled by read() returning -1

while (b != -1)

{

//do something… b = in.read();

}

in.close();

•         We’ve omitted exception handling in the previous examples

•         Almost all methods on the I/O classes (including constructors) can throw an IOException or a subclass.

•         Always wrap I/O code in try…catch blocks to handle errors.

I/O – OutputStream

OutputStream out = null; try

{

OutputStream inner = new FileOutputStream(“c:\\temp\\myfile.txt”); out = new BufferedOutputStream(inner);

//write data to the file } catch (IOException e)

{

e.printStackTrace();

}

finally

{

try { out.close(); } catch (Exception e) {}

}