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  /***
58   * BranchHandle is returned by specialized InstructionList.append() whenever a
59   * BranchInstruction is appended. This is useful when the target of this
60   * instruction is not known at time of creation and must be set later
61   * via setTarget().
62   *
63   * @see InstructionHandle
64   * @see Instruction
65   * @see InstructionList
66   * @version $Id: BranchHandle.java,v 1.1.1.1 2001/10/29 20:00:06 jvanzyl Exp $
67   * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
68   */
69  public final class BranchHandle extends InstructionHandle {
70    private BranchInstruction bi; // An alias in fact, but saves lots of casts
71  
72    private BranchHandle(BranchInstruction i) {
73      super(i);
74      bi = i;
75    }
76  
77    /*** Factory methods.
78     */
79    private static BranchHandle bh_list = null; // List of reusable handles
80  
81    static final BranchHandle getBranchHandle(BranchInstruction i) {
82      if(bh_list == null)
83        return new BranchHandle(i);
84      else {
85        BranchHandle bh = bh_list;
86        bh_list = (BranchHandle)bh.next;
87  
88        bh.setInstruction(i);
89  
90        return bh;
91      }
92    }
93    
94    /*** Handle adds itself to the list of resuable handles.
95     */
96    protected void addHandle() {
97      next    = bh_list;
98      bh_list = this;
99    }
100 
101   /* Override InstructionHandle methods: delegate to branch instruction.
102    * Through this overriding all access to the private i_position field should
103    * be prevented.
104    */
105   public int getPosition() { return bi.position; }
106 
107   void setPosition(int pos) {
108     i_position = bi.position = pos;
109   }
110 
111   protected int updatePosition(int offset, int max_offset) {
112     int x = bi.updatePosition(offset, max_offset);
113     i_position = bi.position;
114     return x;
115   }
116 
117   /***
118    * Pass new target to instruction.
119    */
120   public void setTarget(InstructionHandle ih) {
121     bi.setTarget(ih);
122   }
123 
124   /***
125    * Update target of instruction.
126    */
127   public void updateTarget(InstructionHandle old_ih, InstructionHandle new_ih) {
128     bi.updateTarget(old_ih, new_ih);
129   }
130 
131   /***
132    * @return target of instruction.
133    */
134   public InstructionHandle getTarget() {
135     return bi.getTarget();
136   }
137 
138   /*** 
139    * Set new contents. Old instruction is disposed and may not be used anymore.
140    */
141   public void setInstruction(Instruction i) {
142     super.setInstruction(i);
143 
144     if(!(i instanceof BranchInstruction))
145       throw new ClassGenException("Assigning " + i +
146 				  " to branch handle which is not a branch instruction");
147 
148     bi = (BranchInstruction)i;
149   }
150 }
151 
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