Transition.java revision 324c4644fee44b9898524c09511bd33c3f12e2df 
1/*
2 * [The "BSD license"]
3 *  Copyright (c) 2010 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 */
28package org.antlr.analysis;
29
30/** A generic transition between any two state machine states.  It defines
31 *  some special labels that indicate things like epsilon transitions and
32 *  that the label is actually a set of labels or a semantic predicate.
33 *  This is a one way link.  It emanates from a state (usually via a list of
34 *  transitions) and has a label/target pair.  I have abstracted the notion
35 *  of a Label to handle the various kinds of things it can be.
36 */
37public class Transition implements Comparable {
38    /** What label must be consumed to transition to target */
39    public Label label;
40
41    /** The target of this transition */
42    public State target;
43
44    public Transition(Label label, State target) {
45        this.label = label;
46        this.target = target;
47    }
48
49    public Transition(int label, State target) {
50        this.label = new Label(label);
51        this.target = target;
52    }
53
54	public boolean isEpsilon() {
55		return label.isEpsilon();
56	}
57
58	public boolean isAction() {
59		return label.isAction();
60	}
61
62    public boolean isSemanticPredicate() {
63        return label.isSemanticPredicate();
64    }
65
66    public int hashCode() {
67        return label.hashCode() + target.stateNumber;
68    }
69
70    public boolean equals(Object o) {
71        Transition other = (Transition)o;
72        return this.label.equals(other.label) &&
73               this.target.equals(other.target);
74    }
75
76    public int compareTo(Object o) {
77        Transition other = (Transition)o;
78        return this.label.compareTo(other.label);
79    }
80
81    public String toString() {
82        return label+"->"+target.stateNumber;
83    }
84}
85