de.mhus.lib.core.io

Class TextReader

java.lang.Object

de.mhus.lib.core.io.TextReader

public class TextReader
extends Object

From: http://www.cs.arizona.edu/people/reges/teachers/TextReader.java Provides a simple interface for standard text reading operations from an input stream. Converts all IOExceptions to RuntimeExceptions, so it should be used only with stable input streams like System.in. Uses lazy evaluation (delaying the reading of the beginning of a new line until necessary) so as to function properly when used with console input. Unlike the standard java.io.BufferedReader, it returns a correct value for ready() with console reading (returning false only if the user enters an end-of-file from the console). Includes a one-character peek ahead facility. TextReader's behavior is similar to that of Pascal's standard input. It has three utilities for processing the input one token at a time (one for words and two for numbers). As in Pascal, these token-processing methods skip leading whitespace, but unlike Pascal, they also skip trailing whitespace on the current input line. Skipping the trailing space allows one to write token-processing programs without worrying about trailing whitespace at the end of a line that might imply that more input is present when it really isn't. TextReader also provides utilities for reading the input one character at a time or one line at a time, in which case whitespace is preserved. As noted above, it also has a utility for peeking one character ahead in the stream. There is also a method for skipping whitespace. A programmer can combine these utilities to define specialized behavior. To simplify differences between operating systems, TextReader skips a "\r" character if it sees it so that the two-character sequence "\r\n" becomes a single "\n" character. It also inserts a virtual "\n" before end-of-file if one is not present. Below is an example of how to construct and manipulate a reader for interactive console input.

 TextReader console = new TextReader(System.in);
 System.out.print("What is your name? ");
 String name = console.readLine();
 System.out.print("Give me two positive numbers, " + name + " --> ");
 double x = console.readDouble();
 double y = console.readDouble();
 System.out.println(x + " to the " + y + " power = " + Math.pow(x, y));
 System.out.print("Give me a positive integer, " + name + " --> ");
 int n = console.readInt();
 System.out.println("2 to the " + n + " = " + (int) Math.pow(2, n));
 

The code above would execute something like this (user input underlined):

 What is your name? <u>John Boy</u>
 Give me two positive numbers, John Boy --> <u>3.4 2.9</u>
 3.4 to the 2.9 power = 34.77673927667935
 Give me a positive integer, John Boy --> <u>14</u>
 2 to the 14 = 16384
 

By default the token-processing methods like readInt consume the newline character at the end of each line, which assumes that newline characters are not significant. There is a utility that allows a programmer to specify that newline characters are significant, in which case they are left in the input stream. For example, the code below reads exactly one line of input, adding up the integers on the line.

 input.eolIsSignificant(true);
 input.skipWhite(false); // in case the line contains just whitespace
 sum = 0;
 while (input.peek() != '\n')
        sum += input.readInt();
 input.readChar(); // to skip past the newline
 

To construct a reader using a file, the potential I/O error must be caught because, for example, the specified file might not exist. Below is an example of how to construct and manipulate a file reader using a specific file name (in this case, project.dat). If an error occurs, the program exits with a runtime exception.

 TextReader input;
 try {
        input = new TextReader(new FileInputStream("project.dat"));
 } catch (IOException e) {
        throw new RuntimeException(e.toString());
 }
 // if you made it to here, then the file exists and is readable
 int sum = 0;
 while (input.ready())
        sum += input.readInt();
 

Below is a variation where the user is prompted for a file name and the program loops until a legal file name is given.

 TextReader console = new TextReader(System.in);
 TextReader input;
 boolean done = false;
 do {
        System.out.print("input file name? ");
        String name = console.readLine();
        try {
                input = new TextReader(new FileInputStream(name));
                done = true;
        } catch (IOException e) {
                System.out.println(e + ", try again");
        }
 } while (!done);
 int sum = 0;
 while (input.ready())
        sum += input.readInt();
 

The previous two code examples use FileInputStream and IOException, which would require you to include the line below at the beginning of your class file.

 import java.io.*;
 

Author:

Stuart Reges

Constructor Summary

Constructors

Constructor and Description
TextReader(InputStream input) Create a text-reading stream.

Method Summary

Modifier and Type	Method and Description
void	eolIsSignificant(boolean flag) Determine whether or not ends of line are treated as tokens.
char	peek() Peek ahead one character.
char	readChar() Read a single character (including whitespace).
double	readDouble() Read the next token as a double.
int	readInt() Read the next token as an integer.
String	readLine() Reads a line of text.
String	readWord() Read the next token delineated by whitespace.
boolean	ready() Tell whether this stream is ready to be read.
void	skipWhite(boolean skipEoln) Skip whitespace.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

TextReader

public TextReader(InputStream input)

Create a text-reading stream.

Parameters:

input - the input stream to read from

Method Detail

readChar

public char readChar()

Read a single character (including whitespace).

Returns:

next character in the stream

Throws:

RuntimeException - if end-of-file

peek

public char peek()

Peek ahead one character.

Returns:

the character that a subsequent call on readChar() would return

Throws:

RuntimeException - if end-of-file

ready

public boolean ready()

Tell whether this stream is ready to be read.

Returns:

true if ready, false if not

readLine

public String readLine()

Reads a line of text.

Returns:

the line of text without the '\n'

Throws:

RuntimeException - if end-of-file

eolIsSignificant

public void eolIsSignificant(boolean flag)

Determine whether or not ends of line are treated as tokens. This method affects only the token-reading methods (readWord, readInt, readDouble).

Parameters:

flag - whether end-of-line characters should be left in stream

skipWhite

public void skipWhite(boolean skipEoln)

Skip whitespace.

Parameters:

skipEoln - whether or not to skip end-of-line characters

readWord

public String readWord()

Read the next token delineated by whitespace.

Returns:

the word read (empty string if end-of-file reached)

readInt

public int readInt()

Read the next token as an integer.

Returns:

next integer in input stream

Throws:

RuntimeException - if no token or next token not an integer

readDouble

public double readDouble()

Read the next token as a double.

Returns:

next double in input stream

Throws:

RuntimeException - if no token or next token not a double