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Java > Open Source Codes > com > sun > org > apache > bcel > internal > generic > InstructionHandle


1 package com.sun.org.apache.bcel.internal.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.
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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
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41  * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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43  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
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45  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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51  * This software consists of voluntary contributions made by many
52  * individuals on behalf of the Apache Software Foundation. For more
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54  * <http://www.apache.org/>.
55  */
56
57 import com.sun.org.apache.bcel.internal.classfile.Utility;
58 import java.util.HashSet JavaDoc;
59 import java.util.Collection JavaDoc;
60 import java.util.HashMap JavaDoc;
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 JavaDoc {
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 JavaDoc targeters;
85   private HashMap JavaDoc 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 JavaDoc();
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 JavaDoc 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 JavaDoc 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 JavaDoc key, Object JavaDoc attr) {
245     if(attributes == null)
246       attributes = new HashMap JavaDoc(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 JavaDoc 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 JavaDoc getAttribute(Object JavaDoc 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 JavaDoc 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 }
285
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