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    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 }