Package org.antlr.runtime.misc

Class 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 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

      • 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)