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  /*
   [The "BSD license"]
   Copyright (c) 2005-2009 Terence Parr
   All rights reserved.
  
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   modification, are permitted provided that the following conditions
   are met:
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      notice, this list of conditions and the following disclaimer.
  2. Redistributions in binary form must reproduce the above copyright
      notice, this list of conditions and the following disclaimer in the
      documentation and/or other materials provided with the distribution.
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      derived from this software without specific prior written permission.
 
  THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 package org.antlr.runtime;

The most common stream of tokens where every token is buffered up and tokens are filtered for a certain channel (the parser will only see these tokens). Even though it buffers all of the tokens, this token stream pulls tokens from the tokens source on demand. In other words, until you ask for a token using consume(), LT(), etc. the stream does not pull from the lexer. The only difference between this stream and BufferedTokenStream superclass is that this stream knows how to ignore off channel tokens. There may be a performance advantage to using the superclass if you don't pass whitespace and comments etc. to the parser on a hidden channel (i.e., you set $channel instead of calling skip() in lexer rules.)

 
 public class CommonTokenStream extends BufferedTokenStream {
    
Skip tokens on any channel but this one; this is how we skip whitespace...
 
     protected int channel = .;
 
     public CommonTokenStream() { ; }
 
     public CommonTokenStream(TokenSource tokenSource) {
         super(tokenSource);
     }
 
     public CommonTokenStream(TokenSource tokenSourceint channel) {
         this(tokenSource);
         this. = channel;
     }

    
Always leave p on an on-channel token.
 
     public void consume() {
         if (  == -1 ) setup();
         ++;
         sync();
         while ( .get().getChannel()!= ) {
             ++;
             sync();
         }
     }
 
     protected Token LB(int k) {
         if ( k==0 || (-k)<0 ) return null;
 
         int i = ;
         int n = 1;
         // find k good tokens looking backwards
         while ( n<=k ) {
             // skip off-channel tokens
             i = skipOffTokenChannelsReverse(i-1);
             n++;
         }
         if ( i<0 ) return null;
         return .get(i);
     }
 
     public Token LT(int k) {
         //System.out.println("enter LT("+k+")");
         if (  == -1 ) setup();
         if ( k == 0 ) return null;
         if ( k < 0 ) return LB(-k);
         int i = ;
         int n = 1; // we know tokens[p] is a good one
         // find k good tokens
         while ( n<k ) {
             // skip off-channel tokens
             i = skipOffTokenChannels(i+1);
            n++;
        }
		if ( i> )  = i;		
        return .get(i);
    }

    
Given a starting index, return the index of the first on-channel token.
    protected int skipOffTokenChannels(int i) {
        sync(i);
        while ( .get(i).getChannel()!= ) { // also stops at EOF (it's onchannel)
            i++;
            sync(i);
        }
        return i;
    }
    protected int skipOffTokenChannelsReverse(int i) {
        while ( i>=0 && ((Token).get(i)).getChannel()!= ) {
            i--;
        }
        return i;
    }
    protected void setup() {
         = 0;
        sync(0);
        int i = 0;
        while ( .get(i).getChannel()!= ) {
            i++;
            sync(i);
        }
         = i;
    }

Count EOF just once.
		int n = 0;
		for (int i = 0; i < .size(); i++) {
			Token t = .get(i);
			if ( t.getChannel()== ) n++;
			if ( t.getType()==. ) break;
		}
		return n;
	}

    
Reset this token stream by setting its token source.
    public void setTokenSource(TokenSource tokenSource) {
        super.setTokenSource(tokenSource);
         = .;
    }
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