Module openj9.dtfj

Package com.ibm.dtfj.javacore.parser.framework.parser

Interface ILookAheadBuffer

All Known Implementing Classes:

LookAheadBuffer

public interface ILookAheadBuffer

Prediction buffer that holds a certain number of tokens. Tokens are consumed when the are matched, and the buffer is kept filled all the time until end of token stream is reached.

Method Summary

Modifier and Type	Method	Description
boolean	allConsumed()
void	consume()	Consumes the first element of the buffer.
void	init()
int	length()
IParserToken	lookAhead(int depth)	Looks ahead by a depth amount.
boolean	match(String type)	Matches a given type to the token type found at the first element of the buffer.
int	maxDepth()
void	setLookAheadDepth(int depth)	Depth of the lookahead can be changed after creation.

Method Detail

match

boolean match(String type)

Matches a given type to the token type found at the first element of the buffer.

Parameters:

type - to match against first element in buffer

Returns:

true if match is successful

consume

void consume()
      throws IOException,
             ScannerException

Consumes the first element of the buffer.

Throws:

ScannerException

IOException

allConsumed

boolean allConsumed()

Returns:

true if all tokens from both the input stream and the lookahead buffer have been consumed

lookAhead

IParserToken lookAhead(int depth)
                throws IOException,
                       ScannerException,
                       IndexOutOfBoundsException

Looks ahead by a depth amount. The lowest depth to look ahead is 1. Note that in some cases, a lookahead may be attempted on an earlier error condition that lead to an empty buffer (e.g., an exception was thrown during a fill process, and although more tokens may remain in the input source, the lookahead value may itself be null. Consequently, the lookahead buffer refills first before attempting the lookahead.

Parameters:

depth - to lookahead

Returns:

token at specified lookahead depth or IndexOutOfBoundsException.

Throws:

ScannerException

IOException

IndexOutOfBoundsException - if depth is outside the depth range of the buffer. Minimum depth is always 1.

length

int length()

maxDepth

int maxDepth()

init

void init()
   throws IOException,
          ScannerException

Throws:

ScannerException

IOException

setLookAheadDepth

void setLookAheadDepth(int depth)
                throws IOException,
                       ScannerException

Depth of the lookahead can be changed after creation.
If the new depth is less that the current depth, no new tokens will be read until the outstanding tokens (current depth - new depth) are first consumed.
If the new depth is greater than the current depth, the lookahead will read new tokens to fill the delta.

Parameters:

depth - to change

Throws:

ScannerException - as increasing the current depth of the buffer requires to fill the buffer to the new length

IOException