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Source code: org/apache/bcel/generic/BranchHandle.java


1   /*
2    * Copyright  2000-2004 The Apache Software Foundation
3    *
4    *  Licensed under the Apache License, Version 2.0 (the "License"); 
5    *  you may not use this file except in compliance with the License.
6    *  You may obtain a copy of the License at
7    *
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    *
10   *  Unless required by applicable law or agreed to in writing, software
11   *  distributed under the License is distributed on an "AS IS" BASIS,
12   *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   *  See the License for the specific language governing permissions and
14   *  limitations under the License. 
15   *
16   */
17  package org.apache.bcel.generic;
18  
19  /**
20   * BranchHandle is returned by specialized InstructionList.append() whenever a
21   * BranchInstruction is appended. This is useful when the target of this
22   * instruction is not known at time of creation and must be set later
23   * via setTarget().
24   *
25   * @see InstructionHandle
26   * @see Instruction
27   * @see InstructionList
28   * @version $Id: BranchHandle.java 386056 2006-03-15 11:31:56Z tcurdt $
29   * @author  <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
30   */
31  public final class BranchHandle extends InstructionHandle {
32  
33      private BranchInstruction bi; // An alias in fact, but saves lots of casts
34  
35  
36      private BranchHandle(BranchInstruction i) {
37          super(i);
38          bi = i;
39      }
40  
41      /** Factory methods.
42       */
43      private static BranchHandle bh_list = null; // List of reusable handles
44  
45  
46      static final BranchHandle getBranchHandle( BranchInstruction i ) {
47          if (bh_list == null) {
48              return new BranchHandle(i);
49          }
50          BranchHandle bh = bh_list;
51          bh_list = (BranchHandle) bh.next;
52          bh.setInstruction(i);
53          return bh;
54      }
55  
56  
57      /** Handle adds itself to the list of resuable handles.
58       */
59      protected void addHandle() {
60          next = bh_list;
61          bh_list = this;
62      }
63  
64  
65      /* Override InstructionHandle methods: delegate to branch instruction.
66       * Through this overriding all access to the private i_position field should
67       * be prevented.
68       */
69      public int getPosition() {
70          return bi.position;
71      }
72  
73  
74      void setPosition( int pos ) {
75          i_position = bi.position = pos;
76      }
77  
78  
79      protected int updatePosition( int offset, int max_offset ) {
80          int x = bi.updatePosition(offset, max_offset);
81          i_position = bi.position;
82          return x;
83      }
84  
85  
86      /**
87       * Pass new target to instruction.
88       */
89      public void setTarget( InstructionHandle ih ) {
90          bi.setTarget(ih);
91      }
92  
93  
94      /**
95       * Update target of instruction.
96       */
97      public void updateTarget( InstructionHandle old_ih, InstructionHandle new_ih ) {
98          bi.updateTarget(old_ih, new_ih);
99      }
100 
101 
102     /**
103      * @return target of instruction.
104      */
105     public InstructionHandle getTarget() {
106         return bi.getTarget();
107     }
108 
109 
110     /** 
111      * Set new contents. Old instruction is disposed and may not be used anymore.
112      */
113     public void setInstruction( Instruction i ) {
114         super.setInstruction(i);
115         if (!(i instanceof BranchInstruction)) {
116             throw new ClassGenException("Assigning " + i
117                     + " to branch handle which is not a branch instruction");
118         }
119         bi = (BranchInstruction) i;
120     }
121 }