Overview of Java I/O

1. Overview of Java I/O

2. Stream • A Program often needs to read/write information from/to outer source/destination. • Outer source/destination can be : • A File in a disk • A Network connection(especially socket connction) • Other memory location(array) • Stream is a abstract connection between outer world and your Java program. As the word “Stream” indicates, it has a direction; incoming or outgoing. • Through incoming stream a sequence of byte or character is flowed into your program. • Through outgoing stream a sequence of byte of character is flushed out to outer destination.

3. consists of one or more streams in java.io package

4. What Stream means to Programmer? Reading: open a stream while more information in the stream read information close the stream Writing: open a stream while more information write information to the stream close the stream

5. Byte Oriented Stream • For reading and writing bytes, Java provides two base classes; InputStream and OutputStream. InputStream abstract int read() int read( byte[] b) int read(byte[] b, int off, int len) int available() void close(), and some more ... OutputStream abstract void write(int b) void write(byte[] b) void write(byte[], int off, int len) void close(); void flush();

6. Character Oriented Stream • For reading and writing characters, Java provides two base classes; Reader and Writer. Reader abstract int read(char[] cbuf, int off, int len) int read() int read(char[] cbuf) abstract void close(), and some more ... Writer abstract void write(char[] cbuf, int off, int len) void write(int c) void write(String str) void write(String str, int off, int len) abstract void close(); abstract void flush();

7. What are all those stream classes for? • See Figure 12-1 and 12-2 in page 628 and 629 of the text book and you’ll find so many classes are derived from base class. • Do not be intimidated by its size!!! No one expect you to remember all the details. • Your life will be much easier when you keep the following in mind. We can classify each class in java.io package into two categories: • sink stream: A stream which directrly interact with source/destination • processing stream: A stream which performs some special processing on top of a sink or another processing stream.

8. What’s Processing Streams for? • Recall that InputStream/Reader defines the methods to read series of bytes or characters only. • Generally sink streams does not offer more methods than its base classes. Then consider the followings. • What if you want to read integer data from stream? • What if you want to read an entire line at a time? • What if you want to open and read compressed file? • Etc. • All these and many other features are made possible by using a series of processing streams.

9. source program Processing Streams Sink Stream program destination Processing Streams Sink Stream

10. import java.io.*; public class IOWrite { public static void main(String args[]) { try { DataOutputStream out = new DataOutputStream( new FileOutputStream(args[0])); }catch (IOException ioe) { System.out.println(“io error”); } out.writeInt(4); out.writeFloat((float)3.4); out.writeChar('h'); out.flush(); out.close(); } }

11. import java.io.*; public class IORead { public void static main(String args[]) { try { DataInputStream in = new DataInputStream( new FileInputStream(args[0])); System.out.println("first integer " + in.readInt()); System.out.println("first float " + in.readFloat()); System.out.println("first char " + in.readChar()); } catch(FileNotFoundException fnf){ System.out.println("can't open "); } catch(IOException ioe) { System.out.println("io error"); } } }