Using Processing Stream

1. Using Processing Stream

2. Predefined Streams • System.in InputStream used to read bytes from the keyboard • System.out PrintStream used to write bytes to the screen • System.err PrintStream used to report errors.

3. import java.io.*; public class StdinRead { public static void main(String args[]) { int i=0; char c; try { do { i = System.in.read(); c = (char)i; System.out.println(c +”(“+i+”)”); }while(i != -1); } catch (IOException ioe) { System.err.println(“IO Error”); } }

4. hello year 2000 h(104) e(101) l(108) l(108) o(111) (32) y(121) e(101) a(97) r(114) (32) 2(50) 0(48) 0(48) 0(48) (10) ?(-1)

5. Reading int, float, double,... • System.in is an InputStream, with which we can only read bytes. • To read in int, float, …, you may want to put a processing stream at the end of stream pipe line. • DataInput is an interface that defines all the methods for this purpose. • readBoolean(), readInt(), readDouble(), …. • DataInputStream is a stream class that implements DataInput interface. • Therefore, to read a java primitive data type from a InputStream, adding DataInputStream as a processing stream is one solution. • However, does this work with System.in ?

6. import java.io.*; public class StdinRead { public static void main(String args[]) { try { DataInputStream din = new DataInputStream(System.in)); do { int value = din.readInt(); System.out.println(value); } while ( value != -1 ) } catch (IOException ioe) { System.err.println(“IO Error”); } } Wrong solution, Not what we expected!!!

7. 2000 2001 2002 2003 2004 2005 218772016 808460338 808464672 842018866 540160048 857748016 808722482 808465677 • To read a java primitive data type from a InputStream, the stream should provide exact data type in its binary form. • However, a keyboard input is not for typing in a java primitive data type in binary form. • Then how do we read various primitive data types from the keyboard?

8. Read everyting as a String • What we expect from keyboard inputs is a sequence of characters. • However System.in is not a Reader stream, but an InputStream. • Therefore, to read in various types of data from the keyboard, we need to take three steps. • Convert InputStream to Reader • Read in each line as a String. • Parse the String and convert it to appropriate type.

9. How to read a line from InputStream • InputStreamReader is the bridge between InputStream and Reader. • InputStreamReader isr = new InputStreamReader(System.in); • With a BufferedReader, we can read a line (as a String) from Reader stream. • BufferedReader breader = new BufferedReader(isr); • Now we can read a String line from the keyboard. • String line = breader.readLine();

10. import java.io.*; class LineReader { BufferedReader breader; LineReader(Reader input) throws IOException { breader = new BufferedReader(input); } public String getLine() throws IOException { return breader.readLine(); } public static void main(String args[]) { try { String line=null; LineReader lreader = new LineReader(new InputStreamReader(System.in)); while ( (line=lreader.getLine()) != null ) System.out.println(line); } catch (IOException ioe) { } } }

11. StringTokenizer • StringTokenizer class allows us to break a String into tokens. • Without any given delimeter, the space will be used as a default delimeter. • “Hello year 2000”, will be broken into “Hello”, “year”, “2000” • StringTokenizer class provides methods for retrieving and checking availability of tokens. • boolean hasMoreTokens(); • String nextToken();

12. import java.io.*; public class InputParser { public void static main(String args[]) { try { LineReader reader = new LineReader(new FileReader(args[0])); String line = null; while ( (line=reader.getLine()) != null ) { StringTokenizer st = new StringTokenizer(line); while ( st.hasMoreTokens() ) { String token = st.nextToken(); // Parse a token // int year = Integer.parseInt(token); } } }catch (IOException e) { } } }