org.antlr.runtime.misc

Class LookaheadStream<T>

java.lang.Object

org.antlr.runtime.misc.FastQueue<T>

org.antlr.runtime.misc.LookaheadStream<T>

Direct Known Subclasses:

CommonTreeNodeStream, UnbufferedTokenStream

public abstract class LookaheadStream<T>
extends FastQueue<T>

A lookahead queue that knows how to mark/release locations in the buffer for backtracking purposes. Any markers force the FastQueue superclass to keep all elements until no more markers; then can reset to avoid growing a huge buffer.

Field Summary

Fields

Modifier and Type	Field and Description
protected int	currentElementIndex Absolute token index.
T	eof Track object returned by nextElement upon end of stream; Return it later when they ask for LT passed end of input.
protected int	lastMarker Track the last mark() call result value for use in rewind().
protected int	markDepth tracks how deep mark() calls are nested
protected T	prevElement This is the LT(-1) element for the first element in FastQueue.data.
static int	UNINITIALIZED_EOF_ELEMENT_INDEX

Fields inherited from class org.antlr.runtime.misc.FastQueue

data, p, range

Constructor Summary

Constructors

Constructor and Description
LookaheadStream()

Method Summary

Methods

Modifier and Type	Method and Description
void	consume() Make sure we have at least one element to remove, even if EOF
void	fill(int n) add n elements to buffer
int	index()
abstract boolean	isEOF(T o)
protected T	LB(int k)
T	LT(int k)
int	mark()
abstract T	nextElement() Implement nextElement to supply a stream of elements to this lookahead buffer.
void	release(int marker)
T	remove() Get and remove first element in queue; override FastQueue.remove(); it's the same, just checks for backtracking.
void	reset()
void	rewind()
void	rewind(int marker)
void	seek(int index) Seek to a 0-indexed absolute token index.
int	size() Size of entire stream is unknown; we only know buffer size from FastQueue.
protected void	syncAhead(int need) Make sure we have 'need' elements from current position p.

Methods inherited from class org.antlr.runtime.misc.FastQueue

add, clear, elementAt, head, range, toString

Methods inherited from class java.lang.Object

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

Field Detail

UNINITIALIZED_EOF_ELEMENT_INDEX

public static final int UNINITIALIZED_EOF_ELEMENT_INDEX

See Also:

Constant Field Values

currentElementIndex

protected int currentElementIndex

Absolute token index. It's the index of the symbol about to be read via LT(1). Goes from 0 to numtokens.

prevElement

protected T prevElement

This is the LT(-1) element for the first element in FastQueue.data.

eof

public T eof

Track object returned by nextElement upon end of stream; Return it later when they ask for LT passed end of input.

lastMarker

protected int lastMarker

Track the last mark() call result value for use in rewind().

markDepth

protected int markDepth

tracks how deep mark() calls are nested

Constructor Detail

LookaheadStream

public LookaheadStream()

Method Detail

reset

public void reset()

Overrides:

reset in class FastQueue<T>

nextElement

public abstract T nextElement()

Implement nextElement to supply a stream of elements to this lookahead buffer. Return EOF upon end of the stream we're pulling from.

See Also:

isEOF(T)

isEOF

public abstract boolean isEOF(T o)

remove

public T remove()

Get and remove first element in queue; override FastQueue.remove(); it's the same, just checks for backtracking.

Overrides:

remove in class FastQueue<T>

consume

public void consume()

Make sure we have at least one element to remove, even if EOF

syncAhead

protected void syncAhead(int need)

Make sure we have 'need' elements from current position p. Last valid p index is data.size()-1. p+need-1 is the data index 'need' elements ahead. If we need 1 element, (p+1-1)==p must be < data.size().

fill

public void fill(int n)

add n elements to buffer

size

public int size()

Size of entire stream is unknown; we only know buffer size from FastQueue.

Overrides:

size in class FastQueue<T>

LT

public T LT(int k)

index

public int index()

mark

public int mark()

release

public void release(int marker)

rewind

public void rewind(int marker)

rewind

public void rewind()

seek

public void seek(int index)

Seek to a 0-indexed absolute token index. Normally used to seek backwards in the buffer. Does not force loading of nodes.

To preserve backward compatibility, this method allows seeking past the end of the currently buffered data. In this case, the input pointer will be moved but the data will only actually be loaded upon the next call to consume() or LT(int) for k>0.

Throws:

IllegalArgumentException - if index is less than 0

UnsupportedOperationException - if index lies before the beginning of the moving window buffer (index < currentElementIndex - p).

LB

protected T LB(int k)