Package net.sherst.io

Class LookAheadReader

java.lang.Object

java.io.Reader

net.sherst.io.LookAheadReader

All Implemented Interfaces:

Closeable, AutoCloseable, Readable

public class LookAheadReader
extends Reader

Wrapper for any Reader which provides look-ahead methods (at, atSkip, atWordSkip, peek) and some useful utility methods (readChar(), atEOF(), skipWhitespaceAndComments()).

Makes most parsing tasks easy and efficient, including parsing without a separate lexer and parsing nested grammars.

The capacity is the maximum lookahead (in number of characters). This must be specified when the LookAheadReader is created. LookAheadReader uses a fast but fixed-size ring buffer.

The intended use is parsing source code from start to finish in one thread. Not thread safe.

Author:

sherstDotNet@yahoo.com

Field Summary

Fields inherited from class java.io.Reader

lock

Constructor Summary

Constructors

Constructor	Description
LookAheadReader(Reader reader)	Creates a new LookAheadReader which wraps the provided Reader with the default lookahead limit of 128 characters.
LookAheadReader(Reader reader, int capacity)	Creates a new LookAheadReader which wraps the provided Reader with specified lookahead limit.

Method Summary

Modifier and Type	Method	Description
boolean	at(char c)	Returns true if the next char that will be read is c.
boolean	at(int n, char c)	Returns true if the nth char that will be read is c, counting from 0 (at(0, 'x') tests the first char that will be read).
boolean	at(String s)	Returns true if the next charss that will be read match the String s.
boolean	atComment()	Returns true if the next chars that will be read is #.
boolean	atEOF()	Returns true if all the charss have been read.
boolean	atEOL()	Returns true if all the next char that will be read is '\n' or '\r' or if atEOF().
boolean	atSkip(char c)	If the next char that will be read is c, returns true and removes c from the input.
boolean	atSkip(String s)	If the next chars that will be read match the String s, returns true and removes the chars from the input.
boolean	atSkipComment()	If the next characters to be read will be a "comment", returns true and removes the comment from the input.
boolean	atSkipWhitespaceChar()	If the next char that will be read will be a white space character, returns true and removes the char from the input.
boolean	atSkipWord(String w)	If the "word" that will be read matches w (and no other word).
boolean	atWhitespace()	Returns true if the next char that will be read will be a white space character.
boolean	atWord(String w)	Returns true if the "word" that will be read matches w (and no other word).
void	close()	Closes the LookAheadReader and the wrapped java.lang.Reader.
static boolean	isDecimalDigit(char c)
static boolean	isIdentifierChar(char c)
static boolean	isIdentifierStart(char c)
static boolean	isWhitespace(char c)
void	mark(int readAheadLimit)	Marks the present position in the stream.
boolean	markSupported()	Returns true if this reader supports the mark(int) operation, which it does, but only up to the maximum capacity of the buffer.
char	peek()	Returns the next char that will be read.
char	peek(int n)	Returns the nth char that will be read, counting from 0 (peek(0) returns the first char that will be read).
int	read()	Reads a single character.
int	read(char[] cbuf, int off, int len)	Reads characters into a portion of an array.
char	readChar()	Reads a single character.
boolean	ready()	Returns true if this reader is ready to be read.
void	reset()	Repositions the reader to the mark.
long	skip(long n)	Skips characters.
void	skipWhitespaceAndComments()	Skips white space and comments.

Methods inherited from class java.io.Reader

nullReader, read, read, transferTo

Methods inherited from class java.lang.Object

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

Constructor Details

LookAheadReader

public LookAheadReader(Reader reader)

Creates a new LookAheadReader which wraps the provided Reader with the default lookahead limit of 128 characters.

Parameters:

reader - the Reader to wrap

LookAheadReader

public LookAheadReader(Reader reader,
 int capacity)

Creates a new LookAheadReader which wraps the provided Reader with specified lookahead limit.

Parameters:

reader - the Reader to wrap

capacity - the look ahead limit (number of characters)

Method Details

isDecimalDigit

public static boolean isDecimalDigit(char c)

isIdentifierChar

public static boolean isIdentifierChar(char c)

isIdentifierStart

public static boolean isIdentifierStart(char c)

isWhitespace

public static boolean isWhitespace(char c)

at

public boolean at(char c)
           throws IOException

Returns true if the next char that will be read is c.

Parameters:

c - the char to test for

Returns:

true if the next char that will be read is c

Throws:

IOException

at

public boolean at(int n,
 char c)
           throws IOException

Returns true if the nth char that will be read is c, counting from 0 (at(0, 'x') tests the first char that will be read).

Parameters:

n -

c - the char to test for

Returns:

true if the nth char that will be read is c

Throws:

IOException

at

public boolean at(String s)
           throws IOException

Returns true if the next charss that will be read match the String s.

Parameters:

s - the String to match

Returns:

true if the next charss that will be read match the String s

Throws:

IOException

atComment

public boolean atComment()
                  throws IOException

Returns true if the next chars that will be read is #.

A "comment" starts with # and runs until the end of the line.

Can easily be overridden to accommodate alternative definitions of "comment".

Throws:

IOException

atEOF

public boolean atEOF()
              throws IOException

Returns true if all the charss have been read.

Returns:

true if all the charss have been read

Throws:

IOException

atEOL

public boolean atEOL()
              throws IOException

Returns true if all the next char that will be read is '\n' or '\r' or if atEOF().

Returns:

true if all the next char that will be read is '\n' or '\r' or if atEOF()

Throws:

IOException

atSkip

public boolean atSkip(char c)
               throws IOException

If the next char that will be read is c, returns true and removes c from the input.

Parameters:

c - the true to test for

Returns:

true if the next char that will be read is c

Throws:

IOException

atSkip

public boolean atSkip(String s)
               throws IOException

If the next chars that will be read match the String s, returns true and removes the chars from the input.

Parameters:

s - the String to match

Returns:

true if the next char that will be read match the String s

Throws:

IOException

atSkipComment

public boolean atSkipComment()
                      throws IOException

If the next characters to be read will be a "comment", returns true and removes the comment from the input.

A "comment" starts with # and runs until the end of the line.

Can easily be overridden to accommodate alternative definitions of "comment".

Throws:

IOException

atSkipWhitespaceChar

public boolean atSkipWhitespaceChar()
                             throws IOException

If the next char that will be read will be a white space character, returns true and removes the char from the input.

Can easily be overridden to accommodate alternative definitions of "white space".

Returns:

true if the next char that will be read will be a white space character

Throws:

IOException

atSkipWord

public boolean atSkipWord(String w)
                   throws IOException

If the "word" that will be read matches w (and no other word). returns true and removes the word from the input. Case sensitive.

A "word" starts with a letter or underscore and contains only letters, underscores and digits.

Can easily be overridden to accommodate alternative definitions of "word".

Parameters:

w - the "word" to match

Returns:

true if the "word" that will be read matches w (and no other word)

Throws:

IOException

atWhitespace

public boolean atWhitespace()
                     throws IOException

Returns true if the next char that will be read will be a white space character.

Can easily be overridden to accommodate alternative definitions of "white space".

Returns:

true if the next char that will be read will be a white space character

Throws:

IOException

atWord

public boolean atWord(String w)
               throws IOException

Returns true if the "word" that will be read matches w (and no other word). Case sensitive.

A "word" starts with a letter or underscore and contains only letters, underscores and digits.

Can easily be overridden to accommodate alternative definitions of "word".

Parameters:

w - the "word" to match

Returns:

true if the "word" that will be read matches w (and no other word)

Throws:

IOException

close

public void close()
           throws IOException

Closes the LookAheadReader and the wrapped java.lang.Reader.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Specified by:

close in class Reader

Throws:

IOException

mark

public void mark(int readAheadLimit)
          throws IOException

Marks the present position in the stream. Subsequent calls to reset() will reposition the stream to this point.

Overrides:

mark in class Reader

Parameters:

readAheadLimit - Limit on the number of characters that may be read while still preserving the mark. After reading this many characters, attempting to reset the stream may fail.

Throws:

IOException - if readAheadLimit exceeds buffer capacity

markSupported

public boolean markSupported()

Returns true if this reader supports the mark(int) operation, which it does, but only up to the maximum capacity of the buffer.

Overrides:

markSupported in class Reader

Returns:

true

peek

public char peek()
          throws IOException

Returns the next char that will be read.

Returns:

the next char that will be read

Throws:

IOException

peek

public char peek(int n)
          throws IOException

Returns the nth char that will be read, counting from 0 (peek(0) returns the first char that will be read).

Returns:

the nth char that will be read

Throws:

IOException

read

public int read()
         throws IOException

Reads a single character. This method will block until a character is available, an I/O error occurs, or the end of the stream is reached.

Overrides:

read in class Reader

Returns:

The character read, as an integer in the range 0 to 65535 (0x00-0xffff), or -1 if the end of the stream has been reached

Throws:

IOException

read

public int read(char[] cbuf,
 int off,
 int len)
         throws IOException

Reads characters into a portion of an array. This method will block until some input is available, an I/O error occurs, or the end of the stream is reached. If len is zero, then no characters are read and 0 is returned; otherwise, there is an attempt to read at least one character. If no character is available because the stream is at its end, the value -1 is returned; otherwise, at least one character is read and stored into cbuf.

Specified by:

read in class Reader

Parameters:

cbuf - Destination buffer

off - Offset at which to start storing characters

len - Maximum number of characters to read

Returns:

The number of characters read, or -1 if the end of the stream has been reached

Throws:

IOException

readChar

public char readChar()
              throws IOException

Reads a single character. This method will block until a character is available, an I/O error occurs, or the end of the stream is reached.

Returns:

The character read, as char, or (char)-1 if the end of the stream has been reached

Throws:

IOException

ready

public boolean ready()
              throws IOException

Returns true if this reader is ready to be read.

Overrides:

ready in class Reader

Returns:

true if the next read() is guaranteed not to block for input, false otherwise. Note that returning false does not guarantee that the next read will block.

Throws:

IOException

reset

public void reset()
           throws IOException

Repositions the reader to the mark.

Overrides:

reset in class Reader

Throws:

IOException - if the reader was not marked or if the mark was invalidated by reading past the read ahead limit.

skip

public long skip(long n)
          throws IOException

Skips characters.

Overrides:

skip in class Reader

Parameters:

n - the number of characters to skip

Returns:

the number of characters actually skipped

Throws:

IOException

skipWhitespaceAndComments

public void skipWhitespaceAndComments()
                               throws IOException

Skips white space and comments.

The class can easily be subclassed to accommodate alternative definitions of white space and comments.

Throws:

IOException