com.mpobjects.bdparsii.tokenizer

Class Lookahead<T>

java.lang.Object

com.mpobjects.bdparsii.tokenizer.Lookahead<T>

Type Parameters:

T - the type of the elements kept in the stream

Direct Known Subclasses:

LookaheadReader, Tokenizer

public abstract class Lookahead<T>
extends Object

Abstract data structure for providing streams of items with a lookahead.

Items provided by subclasses of this are processed one after each other. However, using next() or next(int) one can peek at upcoming items without consuming the current one.

Field Summary

Fields

Modifier and Type	Field and Description
protected T	endOfInputIndicator Once the end of the underlying input was reached, an end of input indicator is created and constantly returned for all calls of current and next.
protected boolean	endReached Determines if the end of the underlying data source has been reached.
protected List<T>	itemBuffer Internal buffer containing items which where already created due to lookaheads.
protected List<ParseError>	problemCollector Used to collect problems which occurred when processing the input.

Constructor Summary

Constructors

Constructor and Description
Lookahead()

Method Summary

Modifier and Type	Method and Description
T	consume() Removes and returns the current item from the stream.
void	consume(int numberOfItems) Consumes (removes) numberOfItems at once.
T	current() Returns the item the stream is currently pointing at.
protected abstract T	endOfInput() Creates the end of input indicator item.
protected abstract T	fetch() Fetches the next item from the stream.
List<ParseError>	getProblemCollector() Provides access to the problem collector used by this instance.
T	next() Returns the next item after the current one in the stream.
T	next(int offset) Returns the next n-th item in the stream.
void	setProblemCollector(List<ParseError> problemCollector) Installs the given problem collector.

Methods inherited from class java.lang.Object

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

Field Detail

itemBuffer

protected List<T> itemBuffer

Internal buffer containing items which where already created due to lookaheads.

endReached

protected boolean endReached

Determines if the end of the underlying data source has been reached.

problemCollector

protected List<ParseError> problemCollector

Used to collect problems which occurred when processing the input. This is used instead of classic exceptions, so that errors can be recovered and we can continue to process to input to check for further errors or problems.

endOfInputIndicator

protected T endOfInputIndicator

Once the end of the underlying input was reached, an end of input indicator is created and constantly returned for all calls of current and next.

Constructor Detail

Lookahead

public Lookahead()

Method Detail

current

public T current()

Returns the item the stream is currently pointing at.

This method does not change the internal state. Therefore it can be called several times and will always return the same result.

Returns:

the item the stream is currently pointing at.

next

public T next()

Returns the next item after the current one in the stream.

This method does not change the internal state. Therefore it can be called several times and will always return the same result.

Returns:

the next item in the stream. This will be the current item, after a call to consume()

next

public T next(int offset)

Returns the next n-th item in the stream.

Calling this method with 0 as parameter, will return the current item. Calling it with 1 will return the same item as a call to next().

This method does not change the internal state. Therefore it can be called several times and will always return the same result.

Parameters:

offset - the number of items to skip

Returns:

the n-th item in the stream

endOfInput

protected abstract T endOfInput()

Creates the end of input indicator item.

This method will be only called once, as the indicator is cached.

Returns:

a special item which marks the end of the input

fetch

protected abstract T fetch()

Fetches the next item from the stream.

Returns:

the next item in the stream or null to indicate that the end was reached

consume

public T consume()

Removes and returns the current item from the stream.

After this method was called, all calls to current() will then return the item, which was previously returned by next()

Returns:

the item which is being removed from the stream

consume

public void consume(int numberOfItems)

Consumes (removes) numberOfItems at once.

Removes the given number of items from the stream.

Parameters:

numberOfItems - the number of items to remove

getProblemCollector

public List<ParseError> getProblemCollector()

Provides access to the problem collector used by this instance.

Returns:

the problem collector used by this class. This returns the internally used list, therefore it should be treat appropriately

setProblemCollector

public void setProblemCollector(List<ParseError> problemCollector)

Installs the given problem collector.

Parameters:

problemCollector - the problem collector to be from now on