StreamTokenizer (Java SE 13 & JDK 13 )
Description: declaration: module: java.base, package: java.io, class: StreamTokenizer
Keywords: java.io.StreamTokenizer class

Module java.base
Package java.io

# Class StreamTokenizer

java.lang.Object
java.io.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

  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 Details

  - ### 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 Details

  - ### 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 Details

  - ### 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`