1   package org.apache.bcel.generic;
2   
3   /* ====================================================================
4    * The Apache Software License, Version 1.1
5    *
6    * Copyright (c) 2001 The Apache Software Foundation.  All rights
7    * reserved.
8    *
9    * Redistribution and use in source and binary forms, with or without
10   * modification, are permitted provided that the following conditions
11   * are met:
12   *
13   * 1. Redistributions of source code must retain the above copyright
14   *    notice, this list of conditions and the following disclaimer.
15   *
16   * 2. Redistributions in binary form must reproduce the above copyright
17   *    notice, this list of conditions and the following disclaimer in
18   *    the documentation and/or other materials provided with the
19   *    distribution.
20   *
21   * 3. The end-user documentation included with the redistribution,
22   *    if any, must include the following acknowledgment:
23   *       "This product includes software developed by the
24   *        Apache Software Foundation (http://www.apache.org/)."
25   *    Alternately, this acknowledgment may appear in the software itself,
26   *    if and wherever such third-party acknowledgments normally appear.
27   *
28   * 4. The names "Apache" and "Apache Software Foundation" and
29   *    "Apache BCEL" must not be used to endorse or promote products
30   *    derived from this software without prior written permission. For
31   *    written permission, please contact apache@apache.org.
32   *
33   * 5. Products derived from this software may not be called "Apache",
34   *    "Apache BCEL", nor may "Apache" appear in their name, without
35   *    prior written permission of the Apache Software Foundation.
36   *
37   * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
38   * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
39   * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
40   * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
41   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
42   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
43   * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
44   * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
45   * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
46   * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
47   * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
48   * SUCH DAMAGE.
49   * ====================================================================
50   *
51   * This software consists of voluntary contributions made by many
52   * individuals on behalf of the Apache Software Foundation.  For more
53   * information on the Apache Software Foundation, please see
54   * <http://www.apache.org/>.
55   */
56  
57  import org.apache.bcel.classfile.Utility;
58  import java.util.HashSet;
59  import java.util.Collection;
60  import java.util.HashMap;
61  
62  /***
63   * Instances of this class give users a handle to the instructions contained in
64   * an InstructionList. Instruction objects may be used more than once within a
65   * list, this is useful because it saves memory and may be much faster.
66   *
67   * Within an InstructionList an InstructionHandle object is wrapped
68   * around all instructions, i.e., it implements a cell in a
69   * doubly-linked list. From the outside only the next and the
70   * previous instruction (handle) are accessible. One
71   * can traverse the list via an Enumeration returned by
72   * InstructionList.elements().
73   *
74   * @version $Id: InstructionHandle.java,v 1.1.1.1 2001/10/29 20:00:19 jvanzyl Exp $
75   * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
76   * @see Instruction
77   * @see BranchHandle
78   * @see InstructionList 
79   */
80  public class InstructionHandle implements java.io.Serializable {
81    InstructionHandle next, prev;  // Will be set from the outside
82    Instruction       instruction;
83    protected int     i_position = -1; // byte code offset of instruction
84    private HashSet   targeters;
85    private HashMap   attributes;
86  
87    public final InstructionHandle getNext()        { return next; }
88    public final InstructionHandle getPrev()        { return prev; }
89    public final Instruction       getInstruction() { return instruction; }
90  
91    /***
92     * Replace current instruction contained in this handle.
93     * Old instruction is disposed using Instruction.dispose().
94     */
95    public void setInstruction(Instruction i) { // Overridden in BranchHandle
96      if(i == null)
97        throw new ClassGenException("Assigning null to handle");
98  
99      if((this.getClass() != BranchHandle.class) && (i instanceof BranchInstruction))
100       throw new ClassGenException("Assigning branch instruction " + i + " to plain handle");
101 
102     if(instruction != null)
103       instruction.dispose();
104 
105     instruction = i;
106   }
107 
108   /***
109    * Temporarily swap the current instruction, without disturbing
110    * anything. Meant to be used by a debugger, implementing
111    * breakpoints. Current instruction is returned.
112    */
113   public Instruction swapInstruction(Instruction i) {
114     Instruction oldInstruction = instruction;
115     instruction = i;
116     return oldInstruction;
117   }
118 
119   /*private*/ protected InstructionHandle(Instruction i) {
120     setInstruction(i);
121   }
122 
123   private static InstructionHandle ih_list = null; // List of reusable handles
124 
125   /*** Factory method.
126    */
127   static final InstructionHandle getInstructionHandle(Instruction i) {
128     if(ih_list == null)
129       return new InstructionHandle(i);
130     else {
131       InstructionHandle ih = ih_list;
132       ih_list = ih.next;
133 
134       ih.setInstruction(i);
135 
136       return ih;
137     }
138   }
139 
140   /***
141    * Called by InstructionList.setPositions when setting the position for every
142    * instruction. In the presence of variable length instructions `setPositions()'
143    * performs multiple passes over the instruction list to calculate the
144    * correct (byte) positions and offsets by calling this function.
145    *
146    * @param offset additional offset caused by preceding (variable length) instructions
147    * @param max_offset the maximum offset that may be caused by these instructions
148    * @return additional offset caused by possible change of this instruction's length
149    */
150   protected int updatePosition(int offset, int max_offset) {
151     i_position += offset;
152     return 0;
153   }
154 
155   /*** @return the position, i.e., the byte code offset of the contained
156    * instruction. This is accurate only after
157    * InstructionList.setPositions() has been called.
158    */
159   public int getPosition() { return i_position; }
160 
161   /*** Set the position, i.e., the byte code offset of the contained
162    * instruction.
163    */
164   void setPosition(int pos) { i_position = pos; }
165 
166   /*** Overridden in BranchHandle
167    */
168   protected void addHandle() {
169     next    = ih_list;
170     ih_list = this;
171   }
172 
173   /***
174    * Delete contents, i.e., remove user access and make handle reusable.
175    */
176   void dispose() {
177     next = prev = null;
178     instruction.dispose();
179     instruction = null;
180     i_position = -1;
181     attributes = null;
182     removeAllTargeters();
183     addHandle();
184   }
185 
186   /*** Remove all targeters, if any.
187    */
188   public void removeAllTargeters() {
189     if(targeters != null)
190       targeters.clear();
191   }
192 
193   /***
194    * Denote this handle isn't referenced anymore by t.
195    */
196   public void removeTargeter(InstructionTargeter t) {
197     targeters.remove(t);
198   }
199   
200   /***
201    * Denote this handle is being referenced by t.
202    */
203   public void addTargeter(InstructionTargeter t) {
204     if(targeters == null)
205       targeters = new HashSet();
206 
207     //if(!targeters.contains(t))
208     targeters.add(t);
209   }
210 
211   public boolean hasTargeters() {
212     return (targeters != null) && (targeters.size() > 0);
213   }
214 
215   /***
216    * @return null, if there are no targeters
217    */
218   public InstructionTargeter[] getTargeters() {
219     if(!hasTargeters())
220       return null;
221     
222     InstructionTargeter[] t = new InstructionTargeter[targeters.size()];
223     targeters.toArray(t);
224     return t;
225   }
226 
227   /*** @return a (verbose) string representation of the contained instruction. 
228    */
229   public String toString(boolean verbose) {
230     return Utility.format(i_position, 4, false, ' ') + ": " + instruction.toString(verbose);
231   }
232 
233   /*** @return a string representation of the contained instruction. 
234    */
235   public String toString() {
236     return toString(true);
237   }
238 
239   /*** Add an attribute to an instruction handle.
240    *
241    * @param key the key object to store/retrieve the attribute
242    * @param attr the attribute to associate with this handle
243    */
244   public void addAttribute(Object key, Object attr) {
245     if(attributes == null)
246       attributes = new HashMap(3);
247     
248     attributes.put(key, attr);
249   }
250 
251   /*** Delete an attribute of an instruction handle.
252    *
253    * @param key the key object to retrieve the attribute
254    */
255   public void removeAttribute(Object key) {
256     if(attributes != null)
257       attributes.remove(key);
258   }
259 
260   /*** Get attribute of an instruction handle.
261    *
262    * @param key the key object to store/retrieve the attribute
263    */
264   public Object getAttribute(Object key) {
265     if(attributes != null)
266       return attributes.get(key);
267 
268     return null;
269   }
270 
271   /*** @return all attributes associated with this handle
272    */
273   public Collection getAttributes() {
274     return attributes.values();
275   }
276   
277   /*** Convenience method, simply calls accept() on the contained instruction.
278    *
279    * @param v Visitor object
280    */
281   public void accept(Visitor v) {
282     instruction.accept(v);
283   }
284 }
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