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Java Fundamental Classes Reference

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The java.io Package
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StreamTokenizer

Name

StreamTokenizer

Synopsis

Class Name:

java.io.StreamTokenizer

Superclass:

java.lang.Object

Immediate Subclasses:

None

Interfaces Implemented:

None

Availability:

JDK 1.0 or later

Description

The StreamTokenizer class performs a lexical analysis on an InputStream object and breaks the stream into tokens. Although StreamTokenizer is not a general-purpose parser, it recognizes tokens that are similar to those used in the Java language. A StreamTokenizer recognizes identifiers, numbers, quoted strings, and various comment styles.

A StreamTokenizer object can be wrapped around an InputStream. In this case, when the StreamTokenizer reads bytes from the stream, the bytes are converted to Unicode characters by simply zero-extending the byte values to 16 bits. As of Java 1.1, a StreamTokenizer can be wrapped around a Reader to eliminate this problem.

The nextToken() method returns the next token from the stream. The rest of the methods in StreamTokenizer control how the object interprets the characters that it reads and tokenizes them.

The parsing functionality of StreamTokenizer is controlled by a table and a number of flags. Each character that is read from the InputStream is in the range '\u0000' to '\uFFFF'. The character value looks up attributes of the character in the table. A character can have zero or more of the following attributes: whitespace, alphabetic, numeric, string quote, and comment character.

By default, a StreamTokenizer recognizes the following:

  • Whitespace characters between '\u0000' and '\u0020'

  • Alphabetic characters from 'a' through 'z', 'A' through 'Z', and '\u00A0' and '\u00FF'.

  • Numeric characters '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '.', and '-'

  • String quote characters "'" and "'"

  • Comment character "/"

Class Summary

public class java.io.StreamTokenizer extends java.lang.Object {
  // Variables
  public double nval;
  public String sval;
  public int ttype;
  public final static int TT_EOF;
  public final static int TT_EOL;
  public final static int TT_NUMBER;
  public final static int TT_WORD;
  // Constructors 
  public StreamTokenizer(InputStream in);           // Deprecated in 1.1
  public StreamTokenizer(Reader in);                // New in 1.1
  // Instance Methods
  public void commentChar(int ch);
  public void eolIsSignificant(boolean flag);
  public int lineno();
  public void lowerCaseMode(boolean flag);
  public int nextToken();
  public void ordinaryChar(int ch);
  public void ordinaryChars(int low, int hi);
  public void parseNumbers();
  public void pushBack();
  public void quoteChar(int ch);
  public void resetSyntax();
  public void slashSlashComments(boolean flag);
  public void slashStarComments(boolean flag);
  public String toString();
  public void whitespaceChars(int low, int hi);
  public void wordChars(int low, int hi);
}

Variables

nval

public double nval

Description

This variable contains the value of a TT_NUMBER token.

sval

public String sval

Description

This variable contains the value of a TT_WORD token.

ttype

public int ttype

Description

This variable indicates the token type. The value is either one of the TT_ constants defined below or the character that has just been parsed from the input stream.

TT_EOF

public final static int TT_EOF = -1

Description

This token type indicates that the end of the stream has been reached.

TT_EOL

public final static int TT_EOL = '\n'

Description

This token type indicates that the end of a line has been reached. The value is not returned by nextToken() unless eolIsSignificant(true) has been called.

TT_NUMBER

public final static int TT_NUMBER = -2

Description

This token type indicates that a number has been parsed. The number is placed in nval.

TT_WORD

public final static int TT_WORD = -3

Description

This token type indicates that a word has been parsed. The word is placed in sval.

Constructors

StreamTokenizer

public StreamTokenizer(InputStream in)

Availability

Deprecated as of JDK 1.1

Parameters

in

The input stream to tokenize.

Description

This constructor creates a StreamTokenizer that reads from the given InputStream. As of JDK 1.1, this method is deprecated and StreamTokenizer(Reader) should be used instead.

public StreamTokenizer(Reader in)

Availability

New as of JDK 1.1

Parameters

in

The reader to tokenize.

Description

This constructor creates a StreamTokenizer that reads from the given Reader.

Instance Methods

commentChar

public void commentChar(int ch)

Parameters

ch

The character to use to indicate comments.

Description

This method tells this StreamTokenizer to treat the given character as the beginning of a comment that ends at the end of the line. The StreamTokenizer ignores all of the characters from the comment character to the end of the line. By default, a StreamTokenizer treats the '/' character as a comment character. This method may be called multiple times if there are multiple characters that begin comment lines.

To specify that a character is not a comment character, use ordinaryChar().

eolIsSignificant

public void eolIsSignificant(boolean flag)

Parameters

flag

A boolean value that specifies whether or not this StreamTokenizer returns TT_EOL tokens.

Description

A StreamTokenizer recognizes "\n", "\r", and "\r\n" as the end of a line. By default, end-of-line characters are treated as whitespace and thus, the StreamTokenizer does not return TT_EOL tokens from nextToken(). Call eolIsSignificant(true) to tell the StreamTokenizer to return TT_EOL tokens.

lineo

public int lineno()

Returns

The current line number.

Description

This method returns the current line number. Line numbers begin at 1.

lowerCaseMode

public void lowerCaseMode(boolean flag)

Parameters

flag

A boolean value that specifies whether or not this StreamTokenizer returns TT_WORD tokens in lowercase.

Description

By default, a StreamTokenizer does not change the case of the words that it parses. However if you call lowerCaseMode(true), whenever nextToken() returns a TT_WORD token, the word in sval is converted to lowercase.

nextToken

public int nextToken() throws IOException

Returns

One of the token types (TT_EOF, TT_EOL, TT_NUMBER, or TT_WORD) or a character code.

Throws

IOException

If any kind of I/O error occurs.

Description

This method reads the next token from the stream. The value returned is the same as the value of the variable ttype. The nextToken() method parses the following tokens:

TT_EOF

The end of the input stream has been reached.

TT_EOL

The end of a line has been reached. The eolIsSignificant() method controls whether end-of-line characters are treated as whitespace or returned as TT_EOL tokens.

TT_NUMBER

A number has been parsed. The value can be found in the variable nval. The parseNumbers() method tells the StreamTokenizer to recognize numbers distinct from words.

TT_WORD

A word has been parsed. The word can be found in the variable sval.

Quoted string

A quoted string has been parsed. The variable ttype is set to the quote character, and sval contains the string itself. You can tell the StreamTokenizer what characters to use as quote characters using quoteChar().

Character

A single character has been parsed. The variable ttype is set to the character value.

ordinaryChar

public void ordinaryChar(int ch)

Parameters

ch

The character to treat normally.

Description

This method causes this StreamTokenizer to treat the given character as an ordinary character. This means that the character has no special significance as a comment, string quote, alphabetic, numeric, or whitespace character. For example, to tell the StreamTokenizer that the slash does not start a single-line comment, use ordinaryChar('/').

ordinaryChars

public void ordinaryChars(int low, int hi)

Parameters

low

The beginning of a range of character values.

hi

The end of a range of character values.

Description

This method tells this StreamTokenizer to treat all of the characters in the given range as ordinary characters. See the description of ordinaryChar() above for more information.

parseNumbers

public void parseNumbers()

Description

This method tells this StreamTokenizer to recognize numbers. The StreamTokenizer constructor calls this method, so the default behavior of a StreamTokenizer is to recognize numbers. This method modifies the syntax table of the StreamTokenizer so that the following characters have the numeric attribute: '1', '2', '3', '4', '5', '6', '7', '8', '9', '0', '.', and '-'

When the parser encounters a token that has the format of a double-precision floating-point number, the token is treated as a number rather than a word. The ttype variable is set to TT_NUMBER, and nval is set to the value of the number.

To use a StreamTokenizer that does not parse numbers, make the above characters ordinary using ordinaryChar() or ordinaryChars():

pushBack

public void pushBack()

Description

This method has the effect of pushing the current token back onto the stream. In other words, after a call to this method, the next call to the nextToken() method returns the same result as the previous call to the nextToken()method without reading any input.

quoteChar

public void quoteChar(int ch)

Parameters

ch

The character to use as a delimiter for quoted strings.

Description

This method tells this StreamTokenizer to treat the given character as the beginning or end of a quoted string. By default, the single-quote character and the double-quote character are string-quote characters. When the parser encounters a string-quote character, the ttype variable is set to the quote character, and sval is set to the actual string. The string consists of all the characters after (but not including) the string-quote character up to (but not including) the next occurrence of the same string-quote character, a line terminator, or the end of the stream.

To specify that a character is not a string-quote character, use ordinaryChar().

resetSyntax

public void resetSyntax()

Description

This method resets this StreamTokenizer, which causes it to treat all characters as ordinary characters. See the description of ordinaryChar() above for more information.

slashSlashComments

public void slashSlashComments(boolean flag)

Parameters

flag

A boolean value that specifies whether or not this StreamTokenizer recognizes double-slash comments (//).

Description

By default, a StreamTokenizer does not recognize double-slash comments. However, if you call slashSlashComments(true), the nextToken() method recognizes and ignores double-slash comments.

slashStarComments

public void slashStarComments(boolean flag)

Parameters

flag

A boolean value that specifies whether or not this StreamTokenizer recognizes slash-star (/* ... */) comments.

Description

By default, a StreamTokenizer does not recognize slash-star comments. However, if you call slashStarComments(true), the nextToken() method recognizes and ignores slash-star comments.

toString

public String toString()

Returns

A String representation of the current token.

Overrides

Object.toString()

Description

This method returns a string representation of the current token recognized by the nextToken() method. This string representation consists of the value of ttype, the value of sval if the token is a word or the value of nval if the token is a number, and the current line number.

whitespaceChars

public void whitespaceChars(int low, int hi)

Parameters

low

The beginning of a range of character values.

hi

The end of a range of character values.

Description

This method causes this StreamTokenizer to treat characters in the specified range as whitespace. The only function of whitespace characters is to separate tokens in the stream.

wordChars

public void wordChars(int low, int hi)

Parameters

low

The beginning of a range of character values.

hi

The end of a range of character values.

Description

This method causes this StreamTokenizer to treat characters in the specified range as characters that are part of a word token, or, in other words, consider the characters to be alphabetic. A word token consists of a sequence of characters that begins with an alphabetic character and is followed by zero or more numeric or alphabetic characters.

Inherited Methods

Method

Inherited From

Method

Inherited From

clone()

Object

equals(Object)

Object

finalize()

Object

getClass()

Object

hashCode()

Object

notify()

Object

notifyAll()

Object

wait()

Object

wait(long)

Object

wait(long, int)

Object

See Also

InputStream, IOException, Reader, StringTokenizer


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