RangeType


1   /* RangeType Copyright (C) 1998-2002 Jochen Hoenicke.
2    *
3    * This program is free software; you can redistribute it and/or modify
4    * it under the terms of the GNU General Public License as published by
5    * the Free Software Foundation; either version 2, or (at your option)
6    * any later version.
7    *
8    * This program is distributed in the hope that it will be useful,
9    * but WITHOUT ANY WARRANTY; without even the implied warranty of
10   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
11   * GNU General Public License for more details.
12   *
13   * You should have received a copy of the GNU General Public License
14   * along with this program; see the file COPYING.  If not, write to
15   * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
16   *
17   * $Id: RangeType.java,v 4.15.2.2 2002/05/28 17:34:22 hoenicke Exp $
18   */
19  
20  package jode.type;
21  import jode.AssertError;
22  import jode.GlobalOptions;
23  import java.util.Hashtable  ;
24  
25  /**
26   * This class represents a set of reference types.  The set contains
27   * all types that are castable to all the bottom types by a widening
28   * cast and to which one of the top types can be casted to by a
29   * widening cast. <br>
30   *
31   * For a totally unknown reference type bottomType is tObject and
32   * topType is tNull.  The bottomType is always guaranteed to be not
33   * tNull.  And all topTypes must be castable to all bottom types with
34   * a widening cast. <br>
35   *
36   * To do intersection on range types, the reference types need three
37   * more operations: specialization, generalization and
38   * createRange. <p>
39   *
40   * specialization chooses all common sub type of two types.  It is
41   * used to find the bottom of the intersected interval. <p>
42   *
43   * generalization chooses the common super type of two types. It
44   * is used to find the top of the intersected interval. <p>
45   *
46   * When the new interval is created with <code>createRangeType</code>
47   * the bottom and top are adjusted so that they only consists of
48   * possible types.  It then decides, if it needs a range type, or if
49   * the reference types already represents all types.
50   *
51   * @author Jochen Hoenicke
52   * @see ReferenceType
53   * @date 98/08/06 */
54  public class RangeType extends Type {
55      /**
56       * The bottom type set.  It is special in that its interpretation
57       * depends on what ReferenceType class it implements:
58       *
59       * <dl>
60       * <dt>ClassInterfacesType</dt>
61       * <dd>All types in this range must be widening castable to all interfaces
62       * and to the class in the bottomType</dd>
63       * <dt>ArrayType</dt>
64       * <dd>All types in this range must be of the bottomType, or the
65       * NullType.</dd>
66       * <dt>NullType</dt>
67       * <dd>not allowed</dd>
68       * </dl> */
69      final ReferenceType bottomType;
70      /**
71       * The top type set.  For each type in this range type, there is a 
72       * top type, that can be casted to this type.
73       */
74      final ReferenceType topType;
75  
76      /**
77       * Create a new range type with the given bottom and top set.
78       */
79      public RangeType(ReferenceType bottomType, 
80               ReferenceType topType) {
81          super(TC_RANGE);
82      if (bottomType == tNull)
83          throw new jode.AssertError("bottom is NULL");
84      this.bottomType = bottomType;
85      this.topType    = topType;
86      }
87  
88      /**
89       * Returns the bottom type set.  All types in this range type can
90       * be casted to all bottom types by a widening cast.
91       * @return the bottom type set 
92       */
93      public ReferenceType getBottom() {
94          return bottomType;
95      }
96  
97      /**
98       * Returns the top type set.  For each type in this range type,
99       * there is a top type, that can be casted to this type.  
100      * @return the top type set
101      */
102     public ReferenceType getTop() {
103         return topType;
104     }
105 
106     
107     /**
108      * Returns the hint type of this range type set.  This returns the
109      * singleton set containing only the first top type, except if it
110      * is null and there is a unique bottom type, in which case it
111      * returns the bottom type.
112      * @return the hint type.  
113      */
114     public Type getHint() {
115     Type bottomHint = bottomType.getHint();
116     Type topHint = topType.getHint();
117     
118     if (topType == tNull && bottomType.equals(bottomHint))
119         return bottomHint;
120 
121     return topHint;
122     }
123 
124     /**
125      * Returns the canonic type of this range type set.  This returns the
126      * singleton set containing only the first top type.
127      * @return the canonic type.  
128      */
129     public Type getCanonic() {
130     return topType.getCanonic();
131     }
132 
133     /**
134      * The set of super types of this type.  This is the set of
135      * super types of the top type.
136      * @return the set of super types.
137      */
138     public Type getSuperType() {
139     return topType.getSuperType();
140     }
141 
142     /**
143      * The set of sub types of this type.  This is the set of
144      * sub types of the bottom types.
145      * @return the set of super types.
146      */
147     public Type getSubType() {
148     return tRange(bottomType, tNull);
149     }
150         
151     /**
152      * Checks if we need to cast to a middle type, before we can cast from
153      * fromType to this type.
154      * @return the middle type, or null if it is not necessary.
155      */
156     public Type getCastHelper(Type fromType) {
157     return topType.getCastHelper(fromType);
158     }
159 
160     public String   getTypeSignature() {
161         if (topType.isClassType() || !bottomType.isValidType())
162             return topType.getTypeSignature();
163         else
164             return bottomType.getTypeSignature();
165     }
166 
167     public Class   getTypeClass() throws ClassNotFoundException   {
168         if (topType.isClassType() || !bottomType.isValidType())
169             return topType.getTypeClass();
170         else
171             return bottomType.getTypeClass();
172     }
173 
174     public String   toString()
175     {
176     return "<" + bottomType + "-" + topType + ">";
177     }
178 
179     public String   getDefaultName() {
180     throw new AssertError("getDefaultName() called on range");
181     }
182 
183     public int hashCode() {
184     int hashcode = topType.hashCode();
185     return (hashcode << 16 | hashcode >>> 16) ^ bottomType.hashCode();
186     }
187 
188     public boolean equals(Object   o) {
189         if (o instanceof RangeType) {
190             RangeType type = (RangeType) o;
191             return topType.equals(type.topType) 
192                 && bottomType.equals(type.bottomType);
193         }
194         return false;
195     }
196 
197     /**
198      * Intersect this type with another type and return the new type.
199      * @param type the other type.
200      * @return the intersection, or tError, if a type conflict happens.
201      */
202     public Type intersection(Type type) {
203     if (type == tError)
204         return type;
205     if (type == Type.tUnknown)
206         return this;
207 
208     Type top, bottom, result;
209     bottom = bottomType.getSpecializedType(type);
210     top = topType.getGeneralizedType(type);
211     if (top.equals(bottom))
212         result = top;
213     else if (top instanceof ReferenceType
214          && bottom instanceof ReferenceType)
215         result = ((ReferenceType)top)
216         .createRangeType((ReferenceType)bottom);
217     else
218         result = tError;
219 
220         if ((GlobalOptions.debuggingFlags & GlobalOptions.DEBUG_TYPES) != 0) {
221         GlobalOptions.err.println("intersecting "+ this +" and "+ type + 
222                       " to " + result);
223     }       
224         return result;
225     }
226 }
227 
228
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