net.percederberg.grammatica.parser
Class ReaderBuffer

java.lang.Object
  net.percederberg.grammatica.parser.ReaderBuffer

All Implemented Interfaces:

java.lang.CharSequence

public class ReaderBuffer
extends java.lang.Object
implements java.lang.CharSequence

A character buffer that automatically reads from an input source stream when needed. This class keeps track of the current position in the buffer and its line and column number in the original input source. It allows unlimited look-ahead of characters in the input, reading and buffering the required data internally. As the position is advanced, the buffer content prior to the current position is subject to removal to make space for reading new content. A few characters before the current position are always kept to enable boundary condition checks.

Since:

1.5

Field Summary

static int

BLOCK_SIZE The stream reading block size.

Constructor Summary

ReaderBuffer(java.io.Reader input)
Creates a new tokenizer character buffer.

Method Summary

char	charAt(int index) Returns a character already in the buffer.
int	columnNumber() Returns the current column number.
void	dispose() Discards all resources used by this buffer.
int	length() Returns the current character buffer length.
int	lineNumber() Returns the current line number.
int	peek(int offset) Returns a character relative to the current position.
int	position() Returns the current position in the buffer.
java.lang.String	read(int offset) Reads the specified number of characters from the current position.
java.lang.CharSequence	subSequence(int start, int end) Returns a character sequence already in the buffer.
java.lang.String	toString() Returns the current content of the buffer as a string.

Methods inherited from class java.lang.Object

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

Field Detail

BLOCK_SIZE

public static final int BLOCK_SIZE

The stream reading block size. All reads from the underlying character stream will be made in multiples of this block size. Also the character buffer size will always be a multiple of this factor.

See Also:

Constant Field Values

Constructor Detail

ReaderBuffer

public ReaderBuffer(java.io.Reader input)

Creates a new tokenizer character buffer.

Parameters:

input - the input source character reader

Method Detail

dispose

public void dispose()

Discards all resources used by this buffer. This will also close the source input stream. Disposing a previously disposed buffer has no effect.

position

public int position()

Returns the current position in the buffer.

Returns:

the current position in the buffer

lineNumber

public int lineNumber()

Returns the current line number. This number is the input source line number of the current position.

Returns:

the current position line number

columnNumber

public int columnNumber()

Returns the current column number. This number is the input source column number of the current position.

Returns:

the current position column number

length

public int length()

Returns the current character buffer length. Note that the length may increase (and decrease) as more characters are read from the input source or removed to free up space.

Specified by:

length in interface java.lang.CharSequence

charAt

public char charAt(int index)
            throws java.lang.IndexOutOfBoundsException

Returns a character already in the buffer. Note that this method may behave in unexpected ways when performing operations that modifies the buffer content.

Specified by:

charAt in interface java.lang.CharSequence

Parameters:

index - the char index, 0 <= index < length()

Returns:

the character at the specified index

Throws:

java.lang.IndexOutOfBoundsException - if the index is negative or not less than length()

subSequence

public java.lang.CharSequence subSequence(int start,
                                          int end)
                                   throws java.lang.IndexOutOfBoundsException

Returns a character sequence already in the buffer. Note that this method may behave in unexpected ways when performing operations that modifies the buffer content.

Specified by:

subSequence in interface java.lang.CharSequence

Parameters:

start - the start index, inclusive

end - the end index, exclusive

Returns:

the character sequence specified

Throws:

java.lang.IndexOutOfBoundsException - if one of the indices were negative or not less than (or equal) than length()

toString

public java.lang.String toString()

Returns the current content of the buffer as a string. Note that content before the current position will also be returned.

Specified by:

toString in interface java.lang.CharSequence

Overrides:

toString in class java.lang.Object

Returns:

the current buffer content

peek

public int peek(int offset)
         throws java.io.IOException

Returns a character relative to the current position. This method may read from the input source and may also trim the buffer content prior to the current position. The result of calling this method may therefore be that the buffer length and content have been modified.

The character offset must be positive, but is allowed to span the entire size of the input source stream. Note that the internal buffer must hold all the intermediate characters, which may be wasteful if the offset is too large.

Parameters:

offset - the character offset, from 0 and up

Returns:

the character found as an integer in the range 0 to 65535 (0x00-0xffff), or -1 if the end of the stream was reached

Throws:

java.io.IOException - if an I/O error occurred

read

public java.lang.String read(int offset)
                      throws java.io.IOException

Reads the specified number of characters from the current position. This will also move the current position forward. This method will not attempt to move beyond the end of the input source stream. When reaching the end of file, the returned string might be shorter than requested. Any remaining characters will always be returned before returning null.

Parameters:

offset - the character offset, from 0 and up

Returns:

the string containing the characters read, or null no more characters remain in the buffer

Throws:

java.io.IOException - if an I/O error occurred