1 /*
   2  * Copyright (c) 2004, 2010, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package sun.tools.jstat;
  27 
  28 import sun.jvmstat.monitor.*;
  29 
  30 /**
  31  * A class implementing the ExpressionEvaluator to resolve unresolved
  32  * symbols in an Expression in the context of the available monitoring data.
  33  * This class also performs some minimal optimizations of the expressions,
  34  * such as simplification of constant subexpressions.
  35  *
  36  * @author Brian Doherty
  37  * @since 1.5
  38  */
  39 public class ExpressionResolver implements ExpressionEvaluator {
  40     private static boolean debug = Boolean.getBoolean("ExpressionResolver.debug");
  41     private MonitoredVm vm;
  42 
  43     ExpressionResolver(MonitoredVm vm) {
  44         this.vm = vm;
  45     }
  46 
  47     /*
  48      * evaluate the given expression. evaluation in this case means
  49      * to resolve the counter names in the expression
  50      */
  51     public Object evaluate(Expression e) throws MonitorException {
  52 
  53         if (e == null) {
  54             return null;
  55         }
  56 
  57         if (debug) {
  58             System.out.println("Resolving Expression:" + e);
  59         }
  60 
  61         if (e instanceof Identifier) {
  62             Identifier id = (Identifier)e;
  63 
  64             // check if it's already resolved
  65             if (id.isResolved()) {
  66                 return id;
  67             }
  68 
  69             // look it up
  70             Monitor m = vm.findByName(id.getName());
  71             if (m == null) {
  72                 if (debug) {
  73                     System.err.println("Warning: Unresolved Symbol: "
  74                                        + id.getName() + " substituted NaN");
  75                 }
  76                 return new Literal(Double.valueOf(Double.NaN));
  77             }
  78             if (m.getVariability() == Variability.CONSTANT) {
  79                 if (debug) {
  80                     System.out.println("Converting constant " + id.getName()
  81                                        + " to literal with value "
  82                                        + m.getValue());
  83                 }
  84                 return new Literal(m.getValue());
  85             }
  86             id.setValue(m);
  87             return id;
  88         }
  89 
  90         if (e instanceof Literal) {
  91             return e;
  92         }
  93 
  94         Expression l = null;
  95         Expression r = null;
  96 
  97         if (e.getLeft() != null) {
  98             l = (Expression)evaluate(e.getLeft());
  99         }
 100         if (e.getRight() != null) {
 101             r = (Expression)evaluate(e.getRight());
 102         }
 103 
 104         if (l != null && r != null) {
 105             if ((l instanceof Literal) && (r instanceof Literal)) {
 106                 Literal ll = (Literal)l;
 107                 Literal rl = (Literal)r;
 108                 boolean warn = false;
 109 
 110                 Double nan = Double.valueOf(Double.NaN);
 111                 if (ll.getValue() instanceof String) {
 112                     warn = true; ll.setValue(nan);
 113                 }
 114                 if (rl.getValue() instanceof String) {
 115                     warn = true; rl.setValue(nan);
 116                 }
 117                 if (debug && warn) {
 118                      System.out.println("Warning: String literal in "
 119                                         + "numerical expression: "
 120                                         + "substitutied NaN");
 121                 }
 122 
 123                 // perform the operation
 124                 Number ln = (Number)ll.getValue();
 125                 Number rn = (Number)rl.getValue();
 126                 double result = e.getOperator().eval(ln.doubleValue(),
 127                                                      rn.doubleValue());
 128                 if (debug) {
 129                     System.out.println("Converting expression " + e
 130                                        + " (left = " + ln.doubleValue() + ")"
 131                                        + " (right = " + rn.doubleValue() + ")"
 132                                        + " to literal value " + result);
 133                 }
 134                 return new Literal(Double.valueOf(result));
 135             }
 136         }
 137 
 138         if (l != null && r == null) {
 139             return l;
 140         }
 141 
 142         e.setLeft(l);
 143         e.setRight(r);
 144 
 145         return e;
 146     }
 147 }