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1   /*
2    * reserved comment block
3    * DO NOT REMOVE OR ALTER!
4    */
5   package com.sun.org.apache.bcel.internal.generic;
6   
7   /* ====================================================================
8    * The Apache Software License, Version 1.1
9    *
10   * Copyright (c) 2001 The Apache Software Foundation.  All rights
11   * reserved.
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14   * modification, are permitted provided that the following conditions
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17   * 1. Redistributions of source code must retain the above copyright
18   *    notice, this list of conditions and the following disclaimer.
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20   * 2. Redistributions in binary form must reproduce the above copyright
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26   *    if any, must include the following acknowledgment:
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29   *    Alternately, this acknowledgment may appear in the software itself,
30   *    if and wherever such third-party acknowledgments normally appear.
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33   *    "Apache BCEL" must not be used to endorse or promote products
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37   * 5. Products derived from this software may not be called "Apache",
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39   *    prior written permission of the Apache Software Foundation.
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59   */
60  
61  /**
62   * BranchHandle is returned by specialized InstructionList.append() whenever a
63   * BranchInstruction is appended. This is useful when the target of this
64   * instruction is not known at time of creation and must be set later
65   * via setTarget().
66   *
67   * @see InstructionHandle
68   * @see Instruction
69   * @see InstructionList
70   * @author  <A HREF="mailto:markus.dahm@berlin.de">M. Dahm</A>
71   */
72  public final class BranchHandle extends InstructionHandle {
73    private BranchInstruction bi; // An alias in fact, but saves lots of casts
74  
75    private BranchHandle(BranchInstruction i) {
76      super(i);
77      bi = i;
78    }
79  
80    /** Factory methods.
81     */
82    private static BranchHandle bh_list = null; // List of reusable handles
83  
84    static final BranchHandle getBranchHandle(BranchInstruction i) {
85      if(bh_list == null)
86        return new BranchHandle(i);
87      else {
88        BranchHandle bh = bh_list;
89        bh_list = (BranchHandle)bh.next;
90  
91        bh.setInstruction(i);
92  
93        return bh;
94      }
95    }
96  
97    /** Handle adds itself to the list of resuable handles.
98     */
99    protected void addHandle() {
100     next    = bh_list;
101     bh_list = this;
102   }
103 
104   /* Override InstructionHandle methods: delegate to branch instruction.
105    * Through this overriding all access to the private i_position field should
106    * be prevented.
107    */
108   public int getPosition() { return bi.position; }
109 
110   void setPosition(int pos) {
111     i_position = bi.position = pos;
112   }
113 
114   protected int updatePosition(int offset, int max_offset) {
115     int x = bi.updatePosition(offset, max_offset);
116     i_position = bi.position;
117     return x;
118   }
119 
120   /**
121    * Pass new target to instruction.
122    */
123   public void setTarget(InstructionHandle ih) {
124     bi.setTarget(ih);
125   }
126 
127   /**
128    * Update target of instruction.
129    */
130   public void updateTarget(InstructionHandle old_ih, InstructionHandle new_ih) {
131     bi.updateTarget(old_ih, new_ih);
132   }
133 
134   /**
135    * @return target of instruction.
136    */
137   public InstructionHandle getTarget() {
138     return bi.getTarget();
139   }
140 
141   /**
142    * Set new contents. Old instruction is disposed and may not be used anymore.
143    */
144   public void setInstruction(Instruction i) {
145     super.setInstruction(i);
146 
147     if(!(i instanceof BranchInstruction))
148       throw new ClassGenException("Assigning " + i +
149                                   " to branch handle which is not a branch instruction");
150 
151     bi = (BranchInstruction)i;
152   }
153 }