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25 
26 package sun.tools.jstat;
27 
28 import java.util.*;
29 import sun.jvmstat.monitor.*;
30 
31 /**
32  * A class implementing the ExpressionEvaluator to evaluate an expression
33  * in the context of the available monitoring data.
34  *
35  * @author Brian Doherty
36  * @since 1.5
37  */
38 public class ExpressionExecuter implements ExpressionEvaluator {
39     private static final boolean debug =
40             Boolean.getBoolean("ExpressionEvaluator.debug");
41     private MonitoredVm vm;
42     private HashMap<String, Object> map = new HashMap<String, Object>();
43 
ExpressionExecuter(MonitoredVm vm)44     ExpressionExecuter(MonitoredVm vm) {
45         this.vm = vm;
46     }
47 
48     /*
49      * evaluate the given expression.
50      */
evaluate(Expression e)51     public Object evaluate(Expression e) {
52         if (e == null) {
53             return null;
54         }
55 
56         if (debug) {
57             System.out.println("Evaluating expression: " + e);
58         }
59 
60         if (e instanceof Literal) {
61             return ((Literal)e).getValue();
62         }
63 
64         if (e instanceof Identifier) {
65             Identifier id = (Identifier)e;
66             if (map.containsKey(id.getName())) {
67                 return map.get(id.getName());
68             } else {
69                 // cache the data values for coherency of the values over
70                 // the life of this expression executer.
71                 Monitor m = (Monitor)id.getValue();
72                 Object v = m.getValue();
73                 map.put(id.getName(), v);
74                 return v;
75             }
76         }
77 
78         Expression l = e.getLeft();
79         Expression r = e.getRight();
80 
81         Operator op = e.getOperator();
82 
83         if (op == null) {
84             return evaluate(l);
85         } else {
86             double lval = ((Number)evaluate(l)).doubleValue();
87             double rval = ((Number)evaluate(r)).doubleValue();
88             double result = op.eval(lval, rval);
89             if (debug) {
90                 System.out.println("Performed Operation: " + lval + op + rval
91                                    + " = " + result);
92             }
93             return Double.valueOf(result);
94         }
95     }
96 }
97