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Java > Open Source Codes > ro > infoiasi > donald > compiler > lexer > Operator


1 package ro.infoiasi.donald.compiler.lexer;
2
3 import java.util.*;
4
5 /** An operator in a regular expression */
6 public class Operator implements Comparable JavaDoc {
7     private char symbol;
8     private OpType type;
9     private int precedence;
10     private static int prec = 0;
11
12     /** The type of operator */
13     private static class OpType {
14         private OpType() { /* nothing*/ }
15         public static final OpType UNARY_LEFT = new OpType();
16         public static final OpType UNARY_RIGHT = new OpType();
17         public static final OpType BINARY = new OpType();
18     }
19
20     private static HashMap ops = new HashMap();
21
22     private Operator(char symbol, OpType type) {
23         this.symbol = symbol;
24         this.type = type;
25         this.precedence = prec--;
26         ops.put(new Character JavaDoc(symbol), this);
27     }
28
29     // operators appear in precedence order (unary should always be on top)
30 public static final Operator ITARAT = new Operator('*', OpType.UNARY_LEFT);
31     public static final Operator CONCAT = new Operator('.', OpType.BINARY);
32     public static final Operator UNION = new Operator('|', OpType.BINARY);
33
34     /** Returns the operator corresponding to the given symbol.
35     If no such operator exists then null is returned. */
36     public static Operator get(char symbol) {
37         return (Operator)ops.get(new Character JavaDoc(symbol));
38     }
39
40     /** Returns the symbol representing the operator */
41     public char getSymbol() {
42         return symbol;
43     }
44
45     public static Iterator iterator() {
46         return ops.values().iterator();
47     }
48
49     public int compareTo(Object JavaDoc obj) {
50         if (obj == null) {
51             throw new NullPointerException JavaDoc();
52         }
53         Operator op = (Operator)obj;
54         return (precedence-op.precedence);
55     }
56
57     /** Returns true is the operator is unary and binds to the expression to its left */
58     public boolean isUnaryLeft() {
59         return type==OpType.UNARY_LEFT;
60     }
61
62     /** Returns true is the operator is unary and binds to the expression to its right */
63     public boolean isUnaryRight() {
64         return type==OpType.UNARY_RIGHT;
65     }
66
67     /** Returns true is the operator is binary */
68     public boolean isBinary() {
69         return type==OpType.BINARY;
70     }
71
72     public static void main(String JavaDoc args[]) throws Exception JavaDoc {
73         System.out.println("Precedence: ");
74         Iterator it = Operator.iterator();
75         Operator op1;
76         Operator op2 = (Operator)it.next();
77         while (it.hasNext()) {
78             op1 = op2;
79             op2 = (Operator)it.next();
80             System.out.print("["+op1.getSymbol()+"]");
81             if (op1.compareTo(op2)<0) {
82                 System.out.print("<");
83             } else if (op1.compareTo(op2)>0) {
84                 System.out.print(">");
85             } else {
86                 System.out.println("==");
87             }
88             System.out.println("["+op2.getSymbol()+"]");
89         }
90     }
91 }
92
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