SymbolTable


1   /*****************************************************************************
2   
3   JEP - Java Math Expression Parser 2.3.0
4         October 3 2004
5         (c) Copyright 2004, Nathan Funk and Richard Morris
6         See LICENSE.txt for license information.
7   
8   *****************************************************************************/
9   package org.nfunk.jep;
10  import java.util.*;
11  
12  /** A Hashtable which holds a list of all variables.
13   * Hevily changed from Jep-2.24 which was just a Hashtable which stored
14   * the values of each variable. Here the Hashtable contains
15   * elements of type {@link Variable Variable} which contain
16   * information about that variable.
17   * Rather than using {@link #get get} the methods
18   * {@link #getValue getValue(String)}, {@link #getVar getVar(String)}
19   * should be used to return the value or variable.
20   * The {@link #put put} method is deprecated and should be replace by one of
21   * <ul>
22   * <li>{@link #addVariable addVariable(String,Object)} adds a variable with a given name and value, returns null if variable already exists.
23   * <li>{@link #addConstant addConstant(String,Object)} adds a 'constant' variable whos value cannot be changed.
24   * <li>{@link #setVarValue setVarValue(String,Object)} sets the value of an existing variable. Returns false if variable does not exist.
25   * <li>{@link #makeVarIfNeeded(String,Object)} if necessary creates a variable and set its value.
26   * <li>{@link #makeVarIfNeeded(String)} if necessary creates a variable. Does not change the value.
27   * </ul>
28   * <p>
29   * Variables which do not have a value set are deamed to be invalid.
30   * When Variables need to be constructed then methods in the {@link VariableFactory}
31   * should be called, which allows different types of variables to be used.
32   * 
33   * @author Rich Morris
34   * Created on 28-Feb-2004
35   */ 
36  public class SymbolTable extends Hashtable
37  {
38      protected VariableFactory vf;
39      /** SymbolTable should always be constructed an associated variable factory. */
40      public SymbolTable(VariableFactory varFac)
41      {
42          vf = varFac;
43      }
44      /** Private default constructors, SymbolTable should always be constructed with an explicit variable factory. */
45      private SymbolTable() {}
46      
47      /**
48       * @deprecated The getValue or getVar methods should be used instead. 
49       */
50      public Object   get(Object   key) { return getValue(key); }
51      
52  
53      /** Finds the value of the variable with the given name. 
54       * Returns null if variable does not exist. */
55      public Object   getValue(Object   key)
56      {
57          Variable var = (Variable) super.get(key);
58          if(var==null) return null;
59          return var.getValue();
60      }
61      
62      /** Finds the variable with given name. 
63      * Returns null if variable does not exist. */
64      public Variable getVar(String   name)
65      {
66          return (Variable) super.get(name);
67      }
68  
69      /**
70       * @deprecated The setVarValue or makeVar methods should be used instead.
71       */
72      public Object   put(Object   key,Object   val)
73      {
74          return makeVarIfNeeded((String  ) key,val);
75      }
76  
77      /**
78       * Sets the value of variable with the given name.
79       * Returns false if variable does not exist or if its value cannot be set.
80       */
81      public boolean setVarValue(String   name,Object   val)
82      {
83          Variable var = (Variable) super.get(name);
84          if(var != null)
85          {
86              return var.setValue(val);
87          } 
88          else return false;
89      }
90  
91      /** Creates a variable with given value.
92       * Returns null if variable already exists.
93       */
94      public Variable addVariable(String   name,Object   val)
95      {
96          Variable var = (Variable) super.get(name);
97          if(var != null) return null;
98          else
99          {
100             var = vf.createVariable(name,val);
101             super.put(name,var);
102         }
103         var.setValidValue(true);
104         return var;
105     }
106 
107     /** Create a constant variable with the given name and value.
108      * Returns null if variable already exists.
109      */
110     public Variable addConstant(String   name,Object   val)
111     {
112         Variable var = addVariable(name,val);
113         if(var != null) var.setIsConstant(true);
114         return var;
115     }
116 
117     /** Create a variable with the given name and value.
118      * It siliently does nothing if the value cannot be set.
119      * @return the Variable.
120      */
121     public Variable makeVarIfNeeded(String   name,Object   val)
122     {
123         Variable var = (Variable) super.get(name);
124         if(var != null)
125         {
126             var.setValue(val);
127             return var; 
128         }
129         else
130         {
131             var = vf.createVariable(name,val);
132             super.put(name,var);
133             return var;
134         }
135     }
136 
137     /** If necessary create a variable with the given name.
138      * If the variable exists its value will not be changed.
139      * @return the Variable.
140      */
141     public Variable makeVarIfNeeded(String   name)
142     {
143         Variable var = (Variable) super.get(name);
144         if(var != null) return var; 
145 
146         var = vf.createVariable(name,null);
147         super.put(name,var);
148         return var;
149     }
150 
151     /**
152      * Returns a list of variables, one per line.
153      */
154     public String   toString()
155     {
156         StringBuffer   sb = new StringBuffer  ();
157         for(Enumeration e = this.elements(); e.hasMoreElements(); ) 
158         {
159             Variable var = (Variable) e.nextElement();
160             sb.append(var.toString());
161             sb.append("\n");
162         }
163         return sb.toString();
164     }
165 
166     /**
167      * Clears the values of all variables.
168      * Finer control is available through the
169      * {@link Variable#setValidValue Variable.setValidValue} method.
170      */
171     public void clearValues()
172     {
173         for(Enumeration e = this.elements(); e.hasMoreElements(); ) 
174         {
175             Variable var = (Variable) e.nextElement();
176             if(!var.isConstant()) var.setValidValue(false);
177         }
178     }
179     /**
180      * Returns the variable factory of this instance.
181      */
182     public VariableFactory getVariableFactory() {
183         return vf;
184     }
185 
186 }
187
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