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25 
26 package sun.tools.jstat;
27 
28 import java.util.*;
29 
30 
31 /**
32  * A typesafe enumeration for describing mathematical operators.
33  *
34  * @author Brian Doherty
35  * @since 1.5
36  */
37 public abstract class Operator {
38 
39     private static int nextOrdinal = 0;
40     private static HashMap<String, Operator> map = new HashMap<String, Operator>();
41 
42     private final String name;
43     private final int ordinal = nextOrdinal++;
44 
Operator(String name)45     private Operator(String name) {
46         this.name = name;
47         map.put(name, this);
48     }
49 
eval(double x, double y)50     protected abstract double eval(double x, double y);
51 
52     /* Operator '+' */
53     public static final Operator PLUS = new Operator("+") {
54         protected double eval(double x, double y) {
55             return x + y;
56         }
57     };
58 
59     /* Operator '-' */
60     public static final Operator MINUS = new Operator("-") {
61         protected double eval(double x, double y) {
62             return x - y;
63         }
64     };
65 
66     /* Operator '/' */
67     public static final Operator DIVIDE = new Operator("/") {
68         protected double eval(double x, double y) {
69             if (y == 0) {
70                 return Double.NaN;
71             }
72             return x / y;
73         }
74     };
75 
76     /* Operator '*' */
77     public static final Operator MULTIPLY = new Operator("*") {
78         protected double eval(double x, double y) {
79             return x * y;
80         }
81     };
82 
83     /**
84      * Returns the string representation of this Operator object.
85      *
86      * @return  the string representation of this Operator object
87      */
toString()88     public String toString() {
89         return name;
90     }
91 
92     /**
93      * Maps a string to its corresponding Operator object.
94      *
95      * @param   s  an string to match against Operator objects.
96      * @return     The Operator object matching the given string.
97      */
toOperator(String s)98     public static Operator toOperator(String s) {
99         return map.get(s);
100     }
101 
102     /**
103      * Returns an enumeration of the keys for this enumerated type
104      *
105      * @param   s  an string to match against Operator objects.
106      * @return     The Operator object matching the given string.
107      */
keySet()108     protected static Set<?> keySet() {
109         return map.keySet();
110     }
111 }
112