Class DoubleScanner

java.lang.Object

DoubleScanner

public class DoubleScanner
extends java.lang.Object

Class: DoubleScanner.
Description: Improves the Scanner class by

• being able to return characters that also serve as delimiters.
• handling "reserved words"

  The ability to return delimiters as tokens is accomplished by providing two classes of delimiters:

  • Whitespace: Specified in a regular expression in the style used by Scanner.
  • Token delimiters: Single characters that serve as delimiters but are returned as tokens. They are specified in a string.

  Example: Suppose that the Whitespace delimiters are standard whites space characters and the token delimiters are +, -, *. /. Then the string:
  5 * 10 + 4 / 10 - 1+2-3*4/5
  will result in the tokens:
  "5", "*", "10", "+", "4", "/", "10", "-", "1", "+", "2", "-", "3", "*", "4", "/", and "5"
  being returned by the DoubleScanner.

  The DobuleScanner can return boolean, char, double, int, and Strings. In addition, if given a sorted list of "reserved" words, it can "return" reserved words by specifying their subscript in the array. It can easily be extended to handle additional types.

  The DoubleScanner operates in the following manner: The Scanner class returns tokens after removing whitespace. The Scanner tokens may include token delimiters. The Scanner's tokens are given to the StringTokenizer along with the string containing token delimiters and told to return the delimiters as well as tokens. It breaks up the scanner tokens into the tokens returned by DoubleScanner.

  The default whitespace delimiter used by the Scanner is as recognized by Character.isWhitespace method. Default white space characters include line feed, return, tab and some other control characters in addition to Unicode space, line separator and the paragraph separator.

  It is inefficient and normally incorrect to treat the same character as whitespace and as a tokenDelimiter. If a token delimiter character is also treated as a white space, the Scanner never will return the character so DoubleScanner can never return the character as a token.

  A scanning operation may block waiting for input.

  A tokenDelimiter String is required by every constructor because this class would inefficiently duplicate the action of the Scanner if tokenDelimiters are not needed.

  DoubleScanner can easily be extended to handle special types of tokens. For example, the following subclass translates the Spanish words "uno", "dos", and "tres" into "one", "two", and "three" by adding two new methods: hasNextUnoDosTresWords( ) and nextUnoDosTresWords( ).

   // **** Imports ****
   import java.io.*;
   import java.util.*;
  
   public class SubDoubleScanner extends DoubleScanner {
     public SubDoubleScanner(String source, String tokenDelimiters) {
        super(source, tokenDelimiters);
     }  // constructor SubDoubleScanner for strings
  
     public boolean hasNextUnoDosTresWords() {
        internalNext();  // make sure next token exists and has been found
         if (! foundNextToken)
          return false;
        // is the token one of the special tokens?
        if (theNextToken.equals("uno"))
           return true;
        else if (theNextToken.equals("dos"))
           return true;
        else if (theNextToken.equals("tres"))
           return true;
        return false;
     } // method hasNextUnoDosTresWords
  
     public String nextUnoDosTresWords() {
        String result;
        internalNext();  // make sure theNextToken has been found
        if (theNextToken == null)
           throw new NoSuchElementException(
                 "DoubleScanner.nextUnoDosTres() cannot find a next token");
        // check out theNextToken
        if (theNextToken.equals("uno"))
           result = "one";
        else if (theNextToken.equals("dos"))
           result = "two";
        else if (theNextToken.equals("tres"))
           result = "three";
        else
           throw new InputMismatchException(
                "DoubleScanner.nextUnoDosTres(): "
                + "The next token is not an uno, dos, tres");
        foundNextToken = false;  // the current token is being used.
        return result;
     } // method nextUnoDosTresWords
  
   }  // class SubDoubleScanner
  

  It is important that each call to a hasNextXxx or nextXXX method begins with a call to internalNext. That method makes sure that the next token is stored in theNextToken and foundNextToken is true. If there is no next token these values are set to null and false. When the token is returned by a nextXXX method, foundNextToken is set to false to signal that theNextToken has already been used and the internalNext method will have to search for the next token the next time it is called.
  
  Revision date: 3/24/2006, correct comment 3/3/2008

Field Summary

Fields

Modifier and Type	Field and Description
static java.lang.String	PUNCTUATION A string containing all the punctuation characters on a standard English keyboard.

Constructor Summary

Constructors

Constructor and Description
DoubleScanner(java.io.File source, java.lang.String tokenDelimiters) Constructs a new DoubleScanner that produces tokens scanned from the specified file.
DoubleScanner(java.io.InputStream source, java.lang.String tokenDelimiters) Constructs a new Scanner that produces tokens scanned from the specified input stream.
DoubleScanner(java.lang.String source, java.lang.String tokenDelimiters) Constructs a new Scanner that produces tokens scanned from the specified string.

Method Summary

Modifier and Type	Method and Description
java.lang.String[]	getReservedWords() Returns the array of reserved words.
java.lang.String	getTokenDelimiters() Returns the tokenDelimiters String.
java.lang.String	getWhiteSpace() Returns the whiteSpace regular expression as a String.
boolean	hasNext() Returns true if this scanner has another token in its input.
boolean	hasNextBoolean() Returns true if the next token in this scanner's input can be interpreted as a boolean value using a case insensitive pattern created from the string "true|false".
boolean	hasNextChar() Returns true if this scanner's has another token and it is a char.
boolean	hasNextDouble() Returns true if this scanner's has another token and it is a double.
boolean	hasNextInt() Returns true if this scanner's has another token and it is an integer.
boolean	hasNextReserved() Returns true if this scanner's has another token and it is a reserved word in the array of reserved words.
java.lang.String	next() Returns the next complete token from this scanner.
boolean	nextBoolean() Scans the next token of the input into a boolean value ("true" or "false") and returns that value.
char	nextChar() Scans the next token of the input as a char.
double	nextDouble() Scans the next token of the input as an double.
int	nextInt() Scans the next token of the input as an int.
int	nextReserved() Scans the next token of the input as a reserved word as specified by a sorted array supplied by the setReservedWords method.
void	setReservedWords(java.lang.String[] reservedWords) Set the reserved list for hasNextReservedWord and nextReservedWord.
void	setTokenDelimiters(java.lang.String tokenDelimiters) Sets a new string that contains the characters that are treated as both tokens and delimiters.
void	setWhiteSpace(java.lang.String whiteSpace) Sets string that acts as a regular expression for a white space .

Methods inherited from class java.lang.Object

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

Field Detail

PUNCTUATION

public static final java.lang.String PUNCTUATION

A string containing all the punctuation characters on a standard English keyboard. It can be used as tokenDelimitor string.

See Also:

Constant Field Values

Constructor Detail

DoubleScanner

public DoubleScanner(java.lang.String source,
                     java.lang.String tokenDelimiters)

Constructs a new Scanner that produces tokens scanned from the specified string. Bytes from the string are converted into characters using the underlying platform's default charset. The tokens are determined by applying the whitespace regular expression and the tokenDelimiter string.

Parameters:

source - - The String to be scanned.

tokenDelimiters - - The string used for tokenDelimiters.

Throws:

java.lang.NullPointerException - if tokenDelimiters is null.

DoubleScanner

public DoubleScanner(java.io.InputStream source,
                     java.lang.String tokenDelimiters)

Constructs a new Scanner that produces tokens scanned from the specified input stream. Bytes from the file are converted into characters using the underlying platform's default charset. The tokens are determined by applying the whitespace regular expression and the tokenDelimiter string.

Parameters:

source - - The InputStream to be scanned.

tokenDelimiters - - The string used for tokenDelimiters.

Throws:

java.lang.NullPointerException - if tokenDelimiters is null.

DoubleScanner

public DoubleScanner(java.io.File source,
                     java.lang.String tokenDelimiters)
              throws java.io.FileNotFoundException

Constructs a new DoubleScanner that produces tokens scanned from the specified file. Bytes from the stream are converted into characters using the underlying platform's default charset. The tokens are determined by applying the whitespace regular expression and the tokenDelimiter string.

Parameters:

source - - A file to be scanned.

tokenDelimiters - - The string used for tokenDelimiters.

Throws:

java.io.FileNotFoundException - - if source file is not found

java.lang.NullPointerException - if tokenDelimiters is null.

Method Detail

hasNext

public boolean hasNext()

Returns true if this scanner has another token in its input. The scanner does not advance past any input. This method may block while waiting for input to scan.

hasNext() uses the following algorithm:
I. Has another token already been found? If so, return true.
II. Otherwise: Use the internalNext method to find the next token and return foundNextToken as specified by that method.

Returns:

true if and only if this double scanner has another token.

next

public java.lang.String next()

Returns the next complete token from this scanner. A complete token is preceded and followed by input that matches the delimiter pattern or a tokenDelimiter. This method may block while waiting for input to scan, even if a previous invocation of hasNext() returned true. If the match is successful, the scanner advances past the input that was matched.

Returns:

The next token.

Throws:

java.util.NoSuchElementException - if there are no more tokens

hasNextChar

public boolean hasNextChar()

Returns true if this scanner's has another token and it is a char. The scanner does not advance past any input. This method may block while waiting for input to scan.

Returns:

true if and only if this double scanner has another token and it is a char.

nextChar

public char nextChar()

Scans the next token of the input as a char. This method will throw InputMismatchException if the next token cannot be translated into a char. If the translation is successful, the scanner advances past the input that was returned.

Note: hasNextChar( ) and nextChar( ) do not have corresponding methods in the Scanner class.

Returns:

the char scanned from the input

Throws:

java.util.InputMismatchException - if the next token is not a char

java.util.NoSuchElementException - if input to the DoubleScanner is exhausted

hasNextBoolean

public boolean hasNextBoolean()

Returns true if the next token in this scanner's input can be interpreted as a boolean value using a case insensitive pattern created from the string "true|false". The scanner does not advance past any input. This method may block while waiting for input to scan.

Returns:

true if and only if this double scanner's next token is a valid boolean value

nextBoolean

public boolean nextBoolean()

Scans the next token of the input into a boolean value ("true" or "false") and returns that value. This method will throw InputMismatchException if the next token cannot be translated into a valid boolean value. If the match is successful, the scanner advances past the input that matched.

Returns:

the boolean scanned from the input

Throws:

java.util.InputMismatchException - if the next token is not a char

java.util.NoSuchElementException - if input to the DoubleScanner is exhausted

hasNextInt

public boolean hasNextInt()

Returns true if this scanner's has another token and it is an integer. The scanner does not advance past any input. This method may block while waiting for input to scan.

Returns:

true if and only if this double scanner has another token and it is an integer.

nextInt

public int nextInt()

Scans the next token of the input as an int. This method will throw InputMismatchException if the next token cannot be translated into a valid int value. If the translation is successful, the scanner advances past the input that was matched.

Returns:

the int scanned from the input

Throws:

java.util.InputMismatchException - if the next token does not match the Integer regular expression, or is out of range

java.util.NoSuchElementException - if input to the DoubleScanner is exhausted

hasNextDouble

public boolean hasNextDouble()

Returns true if this scanner's has another token and it is a double. The scanner does not advance past any input. This method may block while waiting for input to scan.

Returns:

true if and only if this double scanner has another token and it is a double

nextDouble

public double nextDouble()

Scans the next token of the input as an double. This method will throw InputMismatchException if the next token cannot be translated into a valid double value. If the translation is successful, the scanner advances past the input that was matched.

Returns:

the double scanned from the input

Throws:

java.util.InputMismatchException - if the next token does not match the double regular expression, or is out of range

java.util.NoSuchElementException - if input to the DoubleScanner is exhausted

hasNextReserved

public boolean hasNextReserved()

Returns true if this scanner's has another token and it is a reserved word in the array of reserved words. The results are indeterminate if the reserved word array is not sorted in ascending order. The sorted reserved word array must be set using setReservedWords before calling this method. Matches are case sensitive. The scanner does not advance past any input. This method may block while waiting for input to scan.

The Scanner class does not have a corresponing method.

Returns:

true if and only if this double scanner has another token and it is a reserved word

Throws:

java.lang.ClassCastException - if the reserved word array is not an array of Strings.

java.lang.NullPointerException - - if the reserved word array has not been set or is null.

nextReserved

public int nextReserved()

Scans the next token of the input as a reserved word as specified by a sorted array supplied by the setReservedWords method. If the next token is a reserved word, it it returns the subscript of the reserved word. This method will throw InputMismatchException if the next token is not a reserved word. If the next token is a reserved word, the scanner advances past the input that matched. The sorted reserved word array must be set using setReservedWords before calling this method. Matches are case sensitive.

Returns:

the subscript of the reserved word

Throws:

java.util.InputMismatchException - if the next token is not in the reserved word array.

java.util.NoSuchElementException - if input to the DoubleScanner is exhausted.

java.lang.ClassCastException - if the reserved word array is not an array of Strings.

setWhiteSpace

public void setWhiteSpace(java.lang.String whiteSpace)

Sets string that acts as a regular expression for a white space .

Parameters:

whiteSpace - - The String containing the regular expression that determines white space.

getWhiteSpace

public java.lang.String getWhiteSpace()

Returns the whiteSpace regular expression as a String.

Returns:

whiteSpace - the String for the regular expression for delimiters that act as white space.

setTokenDelimiters

public void setTokenDelimiters(java.lang.String tokenDelimiters)

Sets a new string that contains the characters that are treated as both tokens and delimiters. E.g. "/+-*".

Parameters:

tokenDelimiters - - a string containing the characters that acts as both tokens and delimiters.

getTokenDelimiters

public java.lang.String getTokenDelimiters()

Returns the tokenDelimiters String.

Returns:

tokenDelimiters the string containing the characters that act as both tokens and delimiters.

getReservedWords

public java.lang.String[] getReservedWords()

Returns the array of reserved words.

Returns:

the array of reserved words.

setReservedWords

public void setReservedWords(java.lang.String[] reservedWords)

Set the reserved list for hasNextReservedWord and nextReservedWord. To be useful for these lists, the reserved word array must be in ascending order.

Parameters:

reservedWords - a sorted list of reserved words;