Package org.antlr.v4.runtime

Class BufferedTokenStream

java.lang.Object
org.antlr.v4.runtime.BufferedTokenStream
All Implemented Interfaces:
IntStream, TokenStream
Direct Known Subclasses:
CommonTokenStream
public class BufferedTokenStream extends Object implements TokenStream
This implementation of TokenStream loads tokens from a TokenSource on-demand, and places the tokens in a buffer to provide access to any previous token by index.

This token stream ignores the value of Token.getChannel(). If your parser requires the token stream filter tokens to only those on a particular channel, such as Token.DEFAULT_CHANNEL or Token.HIDDEN_CHANNEL, use a filtering token stream such a CommonTokenStream.

Tokens are fetched lazily as the cursor advances (via sync(int)), so lexer errors surface interleaved with parser recovery in the historic order. Call fill() explicitly when a full buffer is required up front. When IntStream.size() is available, setup and fill() may pre-size the internal list capacity without changing fetch ordering.

  • Field Details

  • Constructor Details

  • Method Details

    • cachedLT1

      final Token cachedLT1()
      Visible for same-package tests.

    • getTokenSource

      public TokenSource getTokenSource()
      Description copied from interface: TokenStream
      Gets the underlying TokenSource which provides tokens for this stream.
      Specified by:
      getTokenSource in interface TokenStream

    • index

      public int index()
      Description copied from interface: IntStream
      Return the index into the stream of the input symbol referred to by LA(1).

      The behavior of this method is unspecified if no call to an initializing method has occurred after this stream was constructed.

      Specified by:
      index in interface IntStream

    • mark

      public int mark()
      Description copied from interface: IntStream
      A mark provides a guarantee that seek() operations will be valid over a "marked range" extending from the index where mark() was called to the current index(). This allows the use of streaming input sources by specifying the minimum buffering requirements to support arbitrary lookahead during prediction.

      The returned mark is an opaque handle (type int) which is passed to release() when the guarantees provided by the marked range are no longer necessary. When calls to mark()/release() are nested, the marks must be released in reverse order of which they were obtained. Since marked regions are used during performance-critical sections of prediction, the specific behavior of invalid usage is unspecified (i.e. a mark is not released, or a mark is released twice, or marks are not released in reverse order from which they were created).

      The behavior of this method is unspecified if no call to an initializing method has occurred after this stream was constructed.

      This method does not change the current position in the input stream.

      The following example shows the use of mark(), release(mark), index(), and seek(index) as part of an operation to safely work within a marked region, then restore the stream position to its original value and release the mark.

       IntStream stream = ...;
 int index = -1;
 int mark = stream.mark();
 try {
   index = stream.index();
   // perform work here...
 } finally {
   if (index != -1) {
     stream.seek(index);
   }
   stream.release(mark);
 }
      Specified by:
      mark in interface IntStream
      Returns:
      An opaque marker which should be passed to release() when the marked range is no longer required.

    • release

      public void release(int marker)
      Description copied from interface: IntStream
      This method releases a marked range created by a call to mark(). Calls to release() must appear in the reverse order of the corresponding calls to mark(). If a mark is released twice, or if marks are not released in reverse order of the corresponding calls to mark(), the behavior is unspecified.

      For more information and an example, see IntStream.mark().

      Specified by:
      release in interface IntStream
      Parameters:
      marker - A marker returned by a call to mark().
      See Also:

    • reset

      @Deprecated public void reset()
      Deprecated.
      Use seek(0) instead.
      This method resets the token stream back to the first token in the buffer. It is equivalent to calling seek(int)(0).
      See Also:

    • seek

      public void seek(int index)
      Description copied from interface: IntStream
      Set the input cursor to the position indicated by index. If the specified index lies past the end of the stream, the operation behaves as though index was the index of the EOF symbol. After this method returns without throwing an exception, then at least one of the following will be true.
      • index() will return the index of the first symbol appearing at or after the specified index. Specifically, implementations which filter their sources should automatically adjust index forward the minimum amount required for the operation to target a non-ignored symbol.
      • LA(1) returns IntStream.EOF
      This operation is guaranteed to not throw an exception if index lies within a marked region. For more information on marked regions, see IntStream.mark(). The behavior of this method is unspecified if no call to an initializing method has occurred after this stream was constructed.
      Specified by:
      seek in interface IntStream
      Parameters:
      index - The absolute index to seek to.

    • size

      public int size()
      Description copied from interface: IntStream
      Returns the total number of symbols in the stream, including a single EOF symbol.
      Specified by:
      size in interface IntStream

    • consume

      public void consume()
      Description copied from interface: IntStream
      Consumes the current symbol in the stream. This method has the following effects:
      • Forward movement: The value of index() before calling this method is less than the value of index() after calling this method.
      • Ordered lookahead: The value of LA(1) before calling this method becomes the value of LA(-1) after calling this method.
      Note that calling this method does not guarantee that index() is incremented by exactly 1, as that would preclude the ability to implement filtering streams (e.g. CommonTokenStream which distinguishes between "on-channel" and "off-channel" tokens).
      Specified by:
      consume in interface IntStream

    • sync

      protected boolean sync(int i)
      Make sure index i in tokens has a token.
      Returns:
      true if a token is located at index i, otherwise false.
      See Also:

    • fetch

      protected int fetch(int n)
      Add n elements to buffer.
      Returns:
      The actual number of elements added to the buffer.

    • get

      public Token get(int i)
      Description copied from interface: TokenStream
      Gets the Token at the specified index in the stream. When the preconditions of this method are met, the return value is non-null.

      The preconditions for this method are the same as the preconditions of IntStream.seek(int). If the behavior of seek(index) is unspecified for the current state and given index, then the behavior of this method is also unspecified.

      The symbol referred to by index differs from seek() only in the case of filtering streams where index lies before the end of the stream. Unlike seek(), this method does not adjust index to point to a non-ignored symbol.

      Specified by:
      get in interface TokenStream

    • get

      public List<Token> get(int start, int stop)
      Get all tokens from start..stop inclusively.

    • LA

      public int LA(int i)
      Description copied from interface: IntStream
      Gets the value of the symbol at offset i from the current position. When i==1, this method returns the value of the current symbol in the stream (which is the next symbol to be consumed). When i==-1, this method returns the value of the previously read symbol in the stream. It is not valid to call this method with i==0, but the specific behavior is unspecified because this method is frequently called from performance-critical code.

      This method is guaranteed to succeed if any of the following are true:

      • i>0
      • i==-1 and index() returns a value greater than the value of index() after the stream was constructed and LA(1) was called in that order. Specifying the current index() relative to the index after the stream was created allows for filtering implementations that do not return every symbol from the underlying source. Specifying the call to LA(1) allows for lazily initialized streams.
      • LA(i) refers to a symbol consumed within a marked region that has not yet been released.

      If i represents a position at or beyond the end of the stream, this method returns IntStream.EOF.

      The return value is unspecified if i<0 and fewer than -i calls to consume() have occurred from the beginning of the stream before calling this method.

      Specified by:
      LA in interface IntStream

    • LB

      protected Token LB(int k)

    • LT

      @NotNull public Token LT(int k)
      Description copied from interface: TokenStream
      Get the Token instance associated with the value returned by LA(k). This method has the same pre- and post-conditions as IntStream.LA(int). In addition, when the preconditions of this method are met, the return value is non-null and the value of LT(k).getType()==LA(k).
      Specified by:
      LT in interface TokenStream
      See Also:

    • adjustSeekIndex

      protected int adjustSeekIndex(int i)
      Allowed derived classes to modify the behavior of operations which change the current stream position by adjusting the target token index of a seek operation. The default implementation simply returns i. If an exception is thrown in this method, the current stream index should not be changed.

      For example, CommonTokenStream overrides this method to ensure that the seek target is always an on-channel token.

      Parameters:
      i - The target token index.
      Returns:
      The adjusted target token index.

    • lazyInit

      protected final void lazyInit()

    • setup

      protected void setup()
      Initialize the token buffer and set p to the first on-channel (or stream-specific) token.

      Tokens are fetched on demand (sync(int)(0) only). Full lexing of the input is intentionally not performed here: eager fill would advance the lexer to EOF before the parser runs, which reorders lexer-vs-parser error notifications (for example token recognition errors appearing before single-token deletion messages). Callers that want the complete buffer should use fill().

      PERF: When IntStream.size() is available, pre-size the token list capacity (~4 chars per token) so later on-demand growth avoids repeated array copies. Capacity sizing does not change fetch order or error interleaving.

    • ensureTokenCapacityFromCharStream

      private void ensureTokenCapacityFromCharStream()
      Pre-size tokens from IntStream.size() when known. No-op for streams that throw UnsupportedOperationException (unbuffered inputs) or when the token list is not an ArrayList.

    • setTokenSource

      public void setTokenSource(TokenSource tokenSource)
      Reset this token stream by setting its token source.

    • getTokens

      public List<Token> getTokens()

    • getTokens

      public List<Token> getTokens(int start, int stop)

    • getTokens

      public List<Token> getTokens(int start, int stop, BitSet types)
      Given a start and stop index, return a List of all tokens in the token type BitSet. Return null if no tokens were found. This method looks at both on and off channel tokens.

    • getTokens

      public List<Token> getTokens(int start, int stop, int ttype)

    • nextTokenOnChannel

      protected int nextTokenOnChannel(int i, int channel)
      Given a starting index, return the index of the next token on channel. Return i if tokens[i] is on channel. Return the index of the EOF token if there are no tokens on channel between i and EOF.

    • previousTokenOnChannel

      protected int previousTokenOnChannel(int i, int channel)
      Given a starting index, return the index of the previous token on channel. Return i if tokens[i] is on channel. Return -1 if there are no tokens on channel between i and 0.

      If i specifies an index at or after the EOF token, the EOF token index is returned. This is due to the fact that the EOF token is treated as though it were on every channel.

    • getHiddenTokensToRight

      public List<Token> getHiddenTokensToRight(int tokenIndex, int channel)
      Collect all tokens on specified channel to the right of the current token up until we see a token on Lexer.DEFAULT_TOKEN_CHANNEL or EOF. If channel is -1, find any non default channel token.

    • getHiddenTokensToRight

      public List<Token> getHiddenTokensToRight(int tokenIndex)
      Collect all hidden tokens (any off-default channel) to the right of the current token up until we see a token on Lexer.DEFAULT_TOKEN_CHANNEL or EOF.

    • getHiddenTokensToLeft

      public List<Token> getHiddenTokensToLeft(int tokenIndex, int channel)
      Collect all tokens on specified channel to the left of the current token up until we see a token on Lexer.DEFAULT_TOKEN_CHANNEL. If channel is -1, find any non default channel token.

    • getHiddenTokensToLeft

      public List<Token> getHiddenTokensToLeft(int tokenIndex)
      Collect all hidden tokens (any off-default channel) to the left of the current token up until we see a token on Lexer.DEFAULT_TOKEN_CHANNEL.

    • filterForChannel

      protected List<Token> filterForChannel(int from, int to, int channel)

    • getSourceName

      public String getSourceName()
      Description copied from interface: IntStream
      Gets the name of the underlying symbol source. This method returns a non-null, non-empty string. If such a name is not known, this method returns IntStream.UNKNOWN_SOURCE_NAME.
      Specified by:
      getSourceName in interface IntStream

    • getText

      @NotNull public String getText()
      Get the text of all tokens in this buffer.
      Specified by:
      getText in interface TokenStream
      Returns:
      The text of all tokens in the stream.

    • getText

      @NotNull public String getText(Interval interval)
      Description copied from interface: TokenStream
      Return the text of all tokens within the specified interval. This method behaves like the following code (including potential exceptions for violating preconditions of TokenStream.get(int), but may be optimized by the specific implementation. 
       TokenStream stream = ...;
 String text = "";
 for (int i = interval.a; i <= interval.b; i++) {
   text += stream.get(i).getText();
 }
      Specified by:
      getText in interface TokenStream
      Parameters:
      interval - The interval of tokens within this stream to get text for.
      Returns:
      The text of all tokens within the specified interval in this stream.

    • getText

      @NotNull public String getText(RuleContext ctx)
      Description copied from interface: TokenStream
      Return the text of all tokens in the source interval of the specified context. This method behaves like the following code, including potential exceptions from the call to TokenStream.getText(Interval), but may be optimized by the specific implementation.

      If ctx.getSourceInterval() does not return a valid interval of tokens provided by this stream, the behavior is unspecified.

       TokenStream stream = ...;
 String text = stream.getText(ctx.getSourceInterval());
      Specified by:
      getText in interface TokenStream
      Parameters:
      ctx - The context providing the source interval of tokens to get text for.
      Returns:
      The text of all tokens within the source interval of ctx.

    • getText

      @NotNull public String getText(Object start, Object stop)
      Description copied from interface: TokenStream
      Return the text of all tokens in this stream between start and stop (inclusive).

      If the specified start or stop token was not provided by this stream, or if the stop occurred before the start token, the behavior is unspecified.

      For streams which ensure that the Token.getTokenIndex() method is accurate for all of its provided tokens, this method behaves like the following code. Other streams may implement this method in other ways provided the behavior is consistent with this at a high level.

       TokenStream stream = ...;
 String text = "";
 for (int i = start.getTokenIndex(); i <= stop.getTokenIndex(); i++) {
   text += stream.get(i).getText();
 }
      Specified by:
      getText in interface TokenStream
      Parameters:
      start - The first token in the interval to get text for.
      stop - The last token in the interval to get text for (inclusive).
      Returns:
      The text of all tokens lying between the specified start and stop tokens.

    • fill

      public void fill()
      Get all tokens from lexer until EOF.