CommonTokenStream.java revision 324c4644fee44b9898524c09511bd33c3f12e2df 
1/*
2 [The "BSD license"]
3 Copyright (c) 2005-2009 Terence Parr
4 All rights reserved.
5
6 Redistribution and use in source and binary forms, with or without
7 modification, are permitted provided that the following conditions
8 are met:
9 1. Redistributions of source code must retain the above copyright
10     notice, this list of conditions and the following disclaimer.
11 2. Redistributions in binary form must reproduce the above copyright
12     notice, this list of conditions and the following disclaimer in the
13     documentation and/or other materials provided with the distribution.
14 3. The name of the author may not be used to endorse or promote products
15     derived from this software without specific prior written permission.
16
17 THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
18 IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
19 OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
20 IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
21 INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
22 NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
23 DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
24 THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
26 THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 */
28
29package org.antlr.runtime;
30
31/** The most common stream of tokens where every token is buffered up
32 *  and tokens are filtered for a certain channel (the parser will only
33 *  see these tokens).
34 *
35 *  Even though it buffers all of the tokens, this token stream pulls tokens
36 *  from the tokens source on demand. In other words, until you ask for a
37 *  token using consume(), LT(), etc. the stream does not pull from the lexer.
38 *
39 *  The only difference between this stream and BufferedTokenStream superclass
40 *  is that this stream knows how to ignore off channel tokens. There may be
41 *  a performance advantage to using the superclass if you don't pass
42 *  whitespace and comments etc. to the parser on a hidden channel (i.e.,
43 *  you set $channel instead of calling skip() in lexer rules.)
44 *
45 *  @see org.antlr.runtime.UnbufferedTokenStream
46 *  @see org.antlr.runtime.BufferedTokenStream
47 */
48public class CommonTokenStream extends BufferedTokenStream {
49    /** Skip tokens on any channel but this one; this is how we skip whitespace... */
50    protected int channel = Token.DEFAULT_CHANNEL;
51
52    public CommonTokenStream() { ; }
53
54    public CommonTokenStream(TokenSource tokenSource) {
55        super(tokenSource);
56    }
57
58    public CommonTokenStream(TokenSource tokenSource, int channel) {
59        this(tokenSource);
60        this.channel = channel;
61    }
62
63    /** Always leave p on an on-channel token. */
64    public void consume() {
65        if ( p == -1 ) setup();
66        p++;
67        sync(p);
68        while ( tokens.get(p).getChannel()!=channel ) {
69            p++;
70            sync(p);
71        }
72    }
73
74    protected Token LB(int k) {
75        if ( k==0 || (p-k)<0 ) return null;
76
77        int i = p;
78        int n = 1;
79        // find k good tokens looking backwards
80        while ( n<=k ) {
81            // skip off-channel tokens
82            i = skipOffTokenChannelsReverse(i-1);
83            n++;
84        }
85        if ( i<0 ) return null;
86        return tokens.get(i);
87    }
88
89    public Token LT(int k) {
90        //System.out.println("enter LT("+k+")");
91        if ( p == -1 ) setup();
92        if ( k == 0 ) return null;
93        if ( k < 0 ) return LB(-k);
94        int i = p;
95        int n = 1; // we know tokens[p] is a good one
96        // find k good tokens
97        while ( n<k ) {
98            // skip off-channel tokens
99            i = skipOffTokenChannels(i+1);
100            n++;
101        }
102		if ( i>range ) range = i;
103        return tokens.get(i);
104    }
105
106    /** Given a starting index, return the index of the first on-channel
107     *  token.
108     */
109    protected int skipOffTokenChannels(int i) {
110        sync(i);
111        while ( tokens.get(i).getChannel()!=channel ) { // also stops at EOF (it's onchannel)
112            i++;
113            sync(i);
114        }
115        return i;
116    }
117
118    protected int skipOffTokenChannelsReverse(int i) {
119        while ( i>=0 && ((Token)tokens.get(i)).getChannel()!=channel ) {
120            i--;
121        }
122        return i;
123    }
124
125	public void reset() {
126		super.reset();
127		p = skipOffTokenChannels(0);
128	}
129
130	protected void setup() {
131        p = 0;
132        sync(0);
133        int i = 0;
134        while ( tokens.get(i).getChannel()!=channel ) {
135            i++;
136            sync(i);
137        }
138        p = i;
139    }
140
141	/** Count EOF just once. */
142	public int getNumberOfOnChannelTokens() {
143		int n = 0;
144		fill();
145		for (int i = 0; i < tokens.size(); i++) {
146			Token t = tokens.get(i);
147			if ( t.getChannel()==channel ) n++;
148			if ( t.getType()==Token.EOF ) break;
149		}
150		return n;
151	}
152
153    /** Reset this token stream by setting its token source. */
154    public void setTokenSource(TokenSource tokenSource) {
155        super.setTokenSource(tokenSource);
156        channel = Token.DEFAULT_CHANNEL;
157    }
158}
159