Class StreamTokenizer

public class StreamTokenizer
extends Object

The StreamTokenizer class takes an input stream and parses it into "tokens", allowing the tokens to be read one at a time. The parsing process is controlled by a table and a number of flags that can be set to various states. The stream tokenizer can recognize identifiers, numbers, quoted strings, and various comment styles.

Each byte read from the input stream is regarded as a character in the range '\u0000' through '\u00FF'. The character value is used to look up five possible attributes of the character: white space, alphabetic, numeric, string quote, and comment character. Each character can have zero or more of these attributes.

In addition, an instance has four flags. These flags indicate:

  • Whether line terminators are to be returned as tokens or treated as white space that merely separates tokens.
  • Whether C-style comments are to be recognized and skipped.
  • Whether C++-style comments are to be recognized and skipped.
  • Whether the characters of identifiers are converted to lowercase.

A typical application first constructs an instance of this class, sets up the syntax tables, and then repeatedly loops calling the nextToken method in each iteration of the loop until it returns the value TT_EOF.

Since:
1.0
See Also:
nextToken(), TT_EOF

Field Summary

Fields
Modifier and Type Field Description
double nval

If the current token is a number, this field contains the value of that number.
String sval

If the current token is a word token, this field contains a string giving the characters of the word token.
static int TT_EOF

A constant indicating that the end of the stream has been read.
static int TT_EOL

A constant indicating that the end of the line has been read.
static int TT_NUMBER

A constant indicating that a number token has been read.
static int TT_WORD

A constant indicating that a word token has been read.
int ttype

After a call to the nextToken method, this field contains the type of the token just read.

Constructor Summary

Constructors
Constructor Description
StreamTokenizer​(InputStream is)

Deprecated.

As of JDK version 1.1, the preferred way to tokenize an input stream is to convert it into a character stream, for example:
StreamTokenizer​(Reader r)

Create a tokenizer that parses the given character stream.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type Method Description
void commentChar​(int ch)

Specified that the character argument starts a single-line comment.
void eolIsSignificant​(boolean flag)

Determines whether or not ends of line are treated as tokens.
int lineno()

Return the current line number.
void lowerCaseMode​(boolean fl)

Determines whether or not word token are automatically lowercased.
int nextToken()

Parses the next token from the input stream of this tokenizer.
void ordinaryChar​(int ch)

Specifies that the character argument is "ordinary" in this tokenizer.
void ordinaryChars​(int low, int hi)

Specifies that all characters c in the range low <= c <= high are "ordinary" in this tokenizer.
void parseNumbers()

Specifies that numbers should be parsed by this tokenizer.
void pushBack()

Causes the next call to the nextToken method of this tokenizer to return the current value in the ttype field, and not to modify the value in the nval or sval field.
void quoteChar​(int ch)

Specifies that matching pairs of this character delimit string constants in this tokenizer.
void resetSyntax()

Resets this tokenizer's syntax table so that all characters are "ordinary."
void slashSlashComments​(boolean flag)

Determines whether or not the tokenizer recognizes C++-style comments.
void slashStarComments​(boolean flag)

Determines whether or not the tokenizer recognizes C-style comments.
String toString()

Returns the string representation of the current stream token and the line number it occurs on.
void whitespaceChars​(int low, int hi)

Specifies that all characters c in the range low <= c <= high are white space characters.
void wordChars​(int low, int hi)

Specifies that all characters c in the range low <= c <= high are word constituents.

Methods declared in class java.lang.Object

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

Field Detail

ttype

public int ttype

After a call to the nextToken method, this field contains the type of the token just read. For a single character token, its value is the single character, converted to an integer. For a quoted string token, its value is the quote character. Otherwise, its value is one of the following:

  • TT_WORD indicates that the token is a word.
  • TT_NUMBER indicates that the token is a number.
  • TT_EOL indicates that the end of line has been read. The field can only have this value if the eolIsSignificant method has been called with the argument true.
  • TT_EOF indicates that the end of the input stream has been reached.

The initial value of this field is -4.

See Also:
eolIsSignificant(boolean), nextToken(), quoteChar(int), TT_EOF, TT_EOL, TT_NUMBER, TT_WORD

TT_EOF

public static final int TT_EOF

A constant indicating that the end of the stream has been read.

See Also:
Constant Field Values

TT_EOL

public static final int TT_EOL

A constant indicating that the end of the line has been read.

See Also:
Constant Field Values

TT_NUMBER

public static final int TT_NUMBER

A constant indicating that a number token has been read.

See Also:
Constant Field Values

TT_WORD

public static final int TT_WORD

A constant indicating that a word token has been read.

See Also:
Constant Field Values

sval

public String sval

If the current token is a word token, this field contains a string giving the characters of the word token. When the current token is a quoted string token, this field contains the body of the string.

The current token is a word when the value of the ttype field is TT_WORD. The current token is a quoted string token when the value of the ttype field is a quote character.

The initial value of this field is null.

See Also:
quoteChar(int), TT_WORD, ttype

nval

public double nval

If the current token is a number, this field contains the value of that number. The current token is a number when the value of the ttype field is TT_NUMBER.

The initial value of this field is 0.0.

See Also:
TT_NUMBER, ttype

Constructor Detail

StreamTokenizer

@Deprecated
public StreamTokenizer​(InputStream is)
Deprecated.
As of JDK version 1.1, the preferred way to tokenize an input stream is to convert it into a character stream, for example: 
Reader r = new BufferedReader(new InputStreamReader(is));
StreamTokenizer st = new StreamTokenizer(r);

Creates a stream tokenizer that parses the specified input stream. The stream tokenizer is initialized to the following default state:

  • All byte values 'A' through 'Z', 'a' through 'z', and '\u00A0' through '\u00FF' are considered to be alphabetic.
  • All byte values '\u0000' through '\u0020' are considered to be white space.
  • '/' is a comment character.
  • Single quote '\'' and double quote '"' are string quote characters.
  • Numbers are parsed.
  • Ends of lines are treated as white space, not as separate tokens.
  • C-style and C++-style comments are not recognized.
Parameters:
is - an input stream.
See Also:
BufferedReader, InputStreamReader, StreamTokenizer(java.io.Reader)

StreamTokenizer

public StreamTokenizer​(Reader r)

Create a tokenizer that parses the given character stream.

Parameters:
r - a Reader object providing the input stream.
Since:
1.1

Method Detail

resetSyntax

public void resetSyntax()

Resets this tokenizer's syntax table so that all characters are "ordinary." See the ordinaryChar method for more information on a character being ordinary.

See Also:
ordinaryChar(int)

wordChars

public void wordChars​(int low,
                      int hi)

Specifies that all characters c in the range low <= c <= high are word constituents. A word token consists of a word constituent followed by zero or more word constituents or number constituents.

Parameters:
low - the low end of the range.
hi - the high end of the range.

whitespaceChars

public void whitespaceChars​(int low,
                            int hi)

Specifies that all characters c in the range low <= c <= high are white space characters. White space characters serve only to separate tokens in the input stream.

Any other attribute settings for the characters in the specified range are cleared.

Parameters:
low - the low end of the range.
hi - the high end of the range.

ordinaryChars

public void ordinaryChars​(int low,
                          int hi)

Specifies that all characters c in the range low <= c <= high are "ordinary" in this tokenizer. See the ordinaryChar method for more information on a character being ordinary.

Parameters:
low - the low end of the range.
hi - the high end of the range.
See Also:
ordinaryChar(int)

ordinaryChar

public void ordinaryChar​(int ch)

Specifies that the character argument is "ordinary" in this tokenizer. It removes any special significance the character has as a comment character, word component, string delimiter, white space, or number character. When such a character is encountered by the parser, the parser treats it as a single-character token and sets ttype field to the character value.

Making a line terminator character "ordinary" may interfere with the ability of a StreamTokenizer to count lines. The lineno method may no longer reflect the presence of such terminator characters in its line count.

Parameters:
ch - the character.
See Also:
ttype

commentChar

public void commentChar​(int ch)

Specified that the character argument starts a single-line comment. All characters from the comment character to the end of the line are ignored by this stream tokenizer.

Any other attribute settings for the specified character are cleared.

Parameters:
ch - the character.

quoteChar

public void quoteChar​(int ch)

Specifies that matching pairs of this character delimit string constants in this tokenizer.

When the nextToken method encounters a string constant, the ttype field is set to the string delimiter and the sval field is set to the body of the string.

If a string quote character is encountered, then a string is recognized, consisting of all characters after (but not including) the string quote character, up to (but not including) the next occurrence of that same string quote character, or a line terminator, or end of file. The usual escape sequences such as "\n" and "\t" are recognized and converted to single characters as the string is parsed.

Any other attribute settings for the specified character are cleared.

Parameters:
ch - the character.
See Also:
nextToken(), sval, ttype

parseNumbers

public void parseNumbers()

Specifies that numbers should be parsed by this tokenizer. The syntax table of this tokenizer is modified so that each of the twelve characters: 

0 1 2 3 4 5 6 7 8 9 . -

has the "numeric" attribute.

When the parser encounters a word token that has the format of a double precision floating-point number, it treats the token as a number rather than a word, by setting the ttype field to the value TT_NUMBER and putting the numeric value of the token into the nval field.

See Also:
nval, TT_NUMBER, ttype

eolIsSignificant

public void eolIsSignificant​(boolean flag)

Determines whether or not ends of line are treated as tokens. If the flag argument is true, this tokenizer treats end of lines as tokens; the nextToken method returns TT_EOL and also sets the ttype field to this value when an end of line is read.

A line is a sequence of characters ending with either a carriage-return character ('\r') or a newline character ('\n'). In addition, a carriage-return character followed immediately by a newline character is treated as a single end-of-line token.

If the flag is false, end-of-line characters are treated as white space and serve only to separate tokens.

Parameters:
flag - true indicates that end-of-line characters are separate tokens; false indicates that end-of-line characters are white space.
See Also:
nextToken(), ttype, TT_EOL

slashStarComments

public void slashStarComments​(boolean flag)

Determines whether or not the tokenizer recognizes C-style comments. If the flag argument is true, this stream tokenizer recognizes C-style comments. All text between successive occurrences of /* and */ are discarded.

If the flag argument is false, then C-style comments are not treated specially.

Parameters:
flag - true indicates to recognize and ignore C-style comments.

slashSlashComments

public void slashSlashComments​(boolean flag)

Determines whether or not the tokenizer recognizes C++-style comments. If the flag argument is true, this stream tokenizer recognizes C++-style comments. Any occurrence of two consecutive slash characters ('/') is treated as the beginning of a comment that extends to the end of the line.

If the flag argument is false, then C++-style comments are not treated specially.

Parameters:
flag - true indicates to recognize and ignore C++-style comments.

lowerCaseMode

public void lowerCaseMode​(boolean fl)

Determines whether or not word token are automatically lowercased. If the flag argument is true, then the value in the sval field is lowercased whenever a word token is returned (the ttype field has the value TT_WORD by the nextToken method of this tokenizer.

If the flag argument is false, then the sval field is not modified.

Parameters:
fl - true indicates that all word tokens should be lowercased.
See Also:
nextToken(), ttype, TT_WORD

nextToken

public int nextToken()
              throws IOException

Parses the next token from the input stream of this tokenizer. The type of the next token is returned in the ttype field. Additional information about the token may be in the nval field or the sval field of this tokenizer.

Typical clients of this class first set up the syntax tables and then sit in a loop calling nextToken to parse successive tokens until TT_EOF is returned.

Returns:
the value of the ttype field.
Throws:
IOException - if an I/O error occurs.
See Also:
nval, sval, ttype

pushBack

public void pushBack()

Causes the next call to the nextToken method of this tokenizer to return the current value in the ttype field, and not to modify the value in the nval or sval field.

See Also:
nextToken(), nval, sval, ttype

lineno

public int lineno()

Return the current line number.

Returns:
the current line number of this stream tokenizer.

toString

public String toString()

Returns the string representation of the current stream token and the line number it occurs on.

The precise string returned is unspecified, although the following example can be considered typical: 

Token['a'], line 10
Overrides:
toString in class Object
Returns:
a string representation of the token
See Also:
nval, sval, ttype