Using Processing Stream

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.

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”); }

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

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 ?

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!!!

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?

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.

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();

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) { }

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();

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) { } }