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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   * Equality of instructions isn't clearly to be defined. You might
21   * wish, for example, to compare whether instructions have the same
22   * meaning. E.g., whether two INVOKEVIRTUALs describe the same
23   * call.<br>The DEFAULT comparator however, considers two instructions
24   * to be equal if they have same opcode and point to the same indexes
25   * (if any) in the constant pool or the same local variable index. Branch
26   * instructions must have the same target.
27   *
28   * @see Instruction
29   * @version $Id: InstructionComparator.java 386056 2006-03-15 11:31:56Z tcurdt $
30   * @author <A HREF="mailto:m.dahm@gmx.de">M. Dahm</A>
31   */
32  public interface InstructionComparator {
33  
34      public static final InstructionComparator DEFAULT = new InstructionComparator() {
35  
36          public boolean equals( Instruction i1, Instruction i2 ) {
37              if (i1.opcode == i2.opcode) {
38                  if (i1 instanceof Select) {
39                      InstructionHandle[] t1 = ((Select) i1).getTargets();
40                      InstructionHandle[] t2 = ((Select) i2).getTargets();
41                      if (t1.length == t2.length) {
42                          for (int i = 0; i < t1.length; i++) {
43                              if (t1[i] != t2[i]) {
44                                  return false;
45                              }
46                          }
47                          return true;
48                      }
49                  } else if (i1 instanceof BranchInstruction) {
50                      return ((BranchInstruction) i1).target == ((BranchInstruction) i2).target;
51                  } else if (i1 instanceof ConstantPushInstruction) {
52                      return ((ConstantPushInstruction) i1).getValue().equals(
53                              ((ConstantPushInstruction) i2).getValue());
54                  } else if (i1 instanceof IndexedInstruction) {
55                      return ((IndexedInstruction) i1).getIndex() == ((IndexedInstruction) i2)
56                              .getIndex();
57                  } else if (i1 instanceof NEWARRAY) {
58                      return ((NEWARRAY) i1).getTypecode() == ((NEWARRAY) i2).getTypecode();
59                  } else {
60                      return true;
61                  }
62              }
63              return false;
64          }
65      };
66  
67  
68      public boolean equals( Instruction i1, Instruction i2 );
69  }