    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 *  Unless required by applicable law or agreed to in writing, software
    012 *  distributed under the License is distributed on an "AS IS" BASIS,
    013 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 *  See the License for the specific language governing permissions and
    015 *  limitations under the License.
    016 *
    017 */
    018package org.apache.bcel.verifier.structurals;
    019
    020
    021import java.util.ArrayList;
    022
    023import org.apache.bcel.generic.InstructionHandle;
    024
    025/**
    026 * An InstructionContext offers convenient access
    027 * to information like control flow successors and
    028 * such.
    029 *
    030 * @version $Id$
    031 */
    032public interface InstructionContext{
    033
    034    /**
    035     * The getTag and setTag methods may be used for
    036     * temporary flagging, such as graph colouring.
    037     * Nothing in the InstructionContext object depends
    038     * on the value of the tag. JustIce does not use it.
    039     *
    040     * @see #setTag(int tag)
    041     */
    042    int getTag();
    043
    044    /**
    045     * The getTag and setTag methods may be used for
    046     * temporary flagging, such as graph colouring.
    047     * Nothing in the InstructionContext object depends
    048     * on the value of the tag. JustIce does not use it.
    049     *
    050     * @see #getTag()
    051     */
    052    void setTag(int tag);
    053
    054    /**
    055     * This method symbolically executes the Instruction
    056     * held in the InstructionContext.
    057     * It "merges in" the incoming execution frame situation
    058     * (see The Java Virtual Machine Specification, 2nd
    059     * edition, page 146).
    060     * By so doing, the outgoing execution frame situation
    061     * is calculated.
    062     *
    063     * This method is JustIce-specific and is usually of
    064     * no sense for users of the ControlFlowGraph class.
    065     * They should use getInstruction().accept(Visitor),
    066     * possibly in conjunction with the ExecutionVisitor.
    067     *
    068     *
    069     * @see ControlFlowGraph
    070     * @see ExecutionVisitor
    071     * @see #getOutFrame(ArrayList)
    072     * @return true -  if and only if the "outgoing" frame situation
    073     * changed from the one before execute()ing.
    074     */
    075    boolean execute(Frame inFrame, ArrayList<InstructionContext> executionPredecessors,
    076            InstConstraintVisitor icv, ExecutionVisitor ev);
    077
    078    Frame getInFrame();
    079
    080    /**
    081     * This method returns the outgoing execution frame situation;
    082     * therefore <B>it has to be calculated by execute(Frame, ArrayList)
    083     * first.</B>
    084     *
    085     * @see #execute(Frame, ArrayList, InstConstraintVisitor, ExecutionVisitor)
    086     */
    087    Frame getOutFrame(ArrayList<InstructionContext> executionPredecessors);
    088
    089    /**
    090     * Returns the InstructionHandle this InstructionContext is wrapped around.
    091     *
    092     * @return The InstructionHandle this InstructionContext is wrapped around.
    093     */
    094    InstructionHandle getInstruction();
    095
    096    /**
    097     * Returns the usual control flow successors.
    098     * @see #getExceptionHandlers()
    099     */
    100    InstructionContext[] getSuccessors();
    101
    102    /**
    103     * Returns the exception handlers that protect this instruction.
    104     * They are special control flow successors.
    105     */
    106    ExceptionHandler[] getExceptionHandlers();
    107}