/* | |
* 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 | |
* | |
* http://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. | |
*/ | |
/* | |
* $Id$ | |
*/ | |
package org.apache.xalan.xsltc.compiler.util; | |
import java.io.DataOutputStream; | |
import java.io.IOException; | |
import org.apache.bcel.Constants; | |
import org.apache.bcel.generic.ConstantPoolGen; | |
import org.apache.bcel.generic.Instruction; | |
import org.apache.bcel.generic.Visitor; | |
/** | |
* A special abstract dummy subclass of | |
* {@link org.apache.bcel.generic.Instruction} used to mark locations of | |
* interest in an {@link org.apache.bcel.generic.InstructionList}. It and | |
* its subclasses are only used as placeholders, and do not contribute to the | |
* actual byte code instruction stream. | |
*/ | |
abstract class MarkerInstruction extends Instruction { | |
/** | |
* Zero-argument constructor. Sets the opcode to an invalid value and | |
* sets the length to zero, as it will not be written as part of the | |
* generated byte code. | |
*/ | |
public MarkerInstruction() { | |
super(Constants.UNDEFINED, (short) 0); | |
} | |
/** | |
* {@link org.apache.bcel.generic.Visitor}s will know nothing about this | |
* kind of {@link org.apche.bcel.generic.Instruction}, so this method does | |
* nothing. | |
*/ | |
public void accept(Visitor v) { | |
} | |
/** | |
* The number of JVM stack entries consumed by the instruction. | |
* This instruction is just a place holder, so it does not consume any | |
* stack entries. | |
* @param cpg The {@link org.apache.bcel.generic.ConstantPoolGen} for the | |
* current {@link org.apache.bcel.generic.ClassGen} | |
* @return <code>0</code> always | |
*/ | |
final public int consumeStack(ConstantPoolGen cpg) { | |
return 0; | |
} | |
/** | |
* The number of JVM stack entries produced by the instruction. | |
* This instruction is just a place holder, so it does not produce any | |
* stack entries. | |
* @param cpg The {@link org.apache.bcel.generic.ConstantPoolGen} for the | |
* current {@link org.apache.bcel.generic.ClassGen} | |
* @return <code>0</code> always | |
*/ | |
final public int produceStack(ConstantPoolGen cpg) { | |
return 0; | |
} | |
/** | |
* Produce a copy of the instruction. By default a | |
* {@link MarkerInstruction} has no parameters, so the base implementation | |
* of {@link #copy()} returns the instruction itself. | |
* @return The instruction itself. | |
*/ | |
public Instruction copy() { | |
return this; | |
} | |
/** | |
* Dump instruction as byte code to stream out. A {@link MarkerInstruction} | |
* has no effect on the generated byte code so it is never emitted to the | |
* output stream. | |
* @param out Output stream | |
*/ | |
final public void dump(DataOutputStream out) throws IOException { | |
} | |
} |