src/main/java/org/apache/bcel/generic/InstructionComparator.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *   https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing,
 * software distributed under the License is distributed on an
 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 * KIND, either express or implied.  See the License for the
 * specific language governing permissions and limitations
 * under the License.
 */
package org.apache.bcel.generic;

/**
 * Equality of instructions isn't clearly to be defined. You might wish, for example, to compare whether instructions
 * have the same meaning. E.g., whether two INVOKEVIRTUALs describe the same call.
 * <p>
 * The DEFAULT comparator however, considers two instructions to be equal if they have same opcode and point to the same
 * indexes (if any) in the constant pool or the same local variable index. Branch instructions must have the same
 * target.
 * </p>
 *
 * @see Instruction
 */
public interface InstructionComparator {

    /**
     * Default instruction comparator.
     */
    InstructionComparator DEFAULT = (i1, i2) -> {
        if (i1.getOpcode() == i2.getOpcode()) {
            if (i1 instanceof BranchInstruction) {
                // BIs are never equal to make targeters work correctly (BCEL-195)
                return false;
//                } else if (i1 == i2) { TODO consider adding this shortcut
//                    return true; // this must be AFTER the BI test
            }
            if (i1 instanceof ConstantPushInstruction) {
                return ((ConstantPushInstruction) i1).getValue().equals(((ConstantPushInstruction) i2).getValue());
            }
            if (i1 instanceof IndexedInstruction) {
                return ((IndexedInstruction) i1).getIndex() == ((IndexedInstruction) i2).getIndex();
            }
            if (i1 instanceof NEWARRAY) {
                return ((NEWARRAY) i1).getTypecode() == ((NEWARRAY) i2).getTypecode();
            }
            return true;
        }
        return false;
    };

    /**
     * Compares two instructions for equality.
     *
     * @param i1 the first instruction.
     * @param i2 the second instruction.
     * @return true if the instructions are equal, false otherwise.
     */
    boolean equals(Instruction i1, Instruction i2);
}