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CharReader.java

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// file:    CharReader.java
// author:  Robert Keller
// purpose: Provide character reader as defined immediately below.

import java.io.*;

/**
 * A simple reader for reading chars one at a time from a String.
 * Both peek() and read() methods are provided.  Any whitespace is
 * is skipped.  For debugging purposes, a trace of characters read
 * can be turned on or off (default is off).
 */

class CharReader extends java.io.StringReader
{
/**
 * Indicate whether tracing is on or off.
 */

boolean traceOn = false;


/**
 * Character returned when end of input reached.
 */

static char nullchar = '\0';


/**
 * Integer returned by StringReader for end of input.
 */

static int eof = -1;


/**
 * Construct a CharReader for a String.
 */

CharReader(String s)
  {
  super(s);
  }


/**
 * Get the next non-whitespace "character",
 * returning nullchar if there are no more characters.  
 */

public char get()
  {
  int character = readNonWhiteSpace();

  if( character == eof )
    {
    if( traceOn )
      {
      System.out.println("geting at end of input, returning null character");
      }
    return nullchar;
    }
  else
    {
    if( traceOn )
      {
      System.out.println("geting: " + (char)character);
      }
    return (char)character;
    }
  }


/**
 * Return the next non-whitespace character, but leave the 
 * character in the input to be gotten again.  If there are no more
 * characters, nullchar is returned.
 */

public char peek()
  {
  try
    {
    mark(1);
    int character = readNonWhiteSpace();
    reset();  

    if( character == eof )
      {
      if( traceOn )
        {
        System.out.println("peeking at end of input, "
                         + "returning null character");
        }
      return nullchar;
      }
    else
      {
      if( traceOn )
        {
        System.out.println("peeking at: " + (char)character);
        }
      return (char)character;
      }
    }
  catch( IOException e )
    {
    return nullchar;
    }
  }


/**
 * Return true if there are more characters to be get, false otherwise.
 */

public boolean hasMore()
  {
  return peek() != nullchar;  
  }


/**
 * Return the remaining input as a String.
 */

public String toString()
  {
  StringBuffer buffer = new StringBuffer();
  
  int character;

  try
    {
    character = super.read();

    // Keep reading until a non-whitespace character is encountered or eof.

    while( character != eof )
      {
      buffer.append((char)character);
      character = super.read();    
      }
    }
  catch( IOException e )
    {
    }

  return buffer.toString();
  }


/**
 * Get the next non-whitespace character,
 * returning nullchar if there are no more characters.  
 */

private int readNonWhiteSpace()
  {
  int character;

  try
    {
    character = super.read();

    // Keep reading until a non-whitespace character is encountered or eof.

    while( character != eof && Character.isWhitespace((char)character) )
      {
      character = super.read();    
      }
    }
  catch( IOException e )
    {
    return nullchar;
    }

  return character;    
  }


/**
 * Set the trace on or off.
 */

public void setTrace(boolean traceOn)
  {
  this.traceOn = traceOn;
  }
}      

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