src/main/java/org/apache/bcel/verifier/structurals/InstructionContext.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
 *
 *      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.
 *
 */
package org.apache.bcel.verifier.structurals;


import java.util.ArrayList;

import org.apache.bcel.generic.InstructionHandle;

/**
 * An InstructionContext offers convenient access
 * to information like control flow successors and
 * such.
 *
 * @version $Id$
 */
public interface InstructionContext{

    /**
     * The getTag and setTag methods may be used for
     * temporary flagging, such as graph colouring.
     * Nothing in the InstructionContext object depends
     * on the value of the tag. JustIce does not use it.
     *
     * @see #setTag(int tag)
     */
    int getTag();

    /**
     * The getTag and setTag methods may be used for
     * temporary flagging, such as graph colouring.
     * Nothing in the InstructionContext object depends
     * on the value of the tag. JustIce does not use it.
     *
     * @see #getTag()
     */
    void setTag(int tag);

    /**
     * This method symbolically executes the Instruction
     * held in the InstructionContext.
     * It "merges in" the incoming execution frame situation
     * (see The Java Virtual Machine Specification, 2nd
     * edition, page 146).
     * By so doing, the outgoing execution frame situation
     * is calculated.
     *
     * This method is JustIce-specific and is usually of
     * no sense for users of the ControlFlowGraph class.
     * They should use getInstruction().accept(Visitor),
     * possibly in conjunction with the ExecutionVisitor.
     *
     *
     * @see ControlFlowGraph
     * @see ExecutionVisitor
     * @see #getOutFrame(ArrayList)
     * @return true -  if and only if the "outgoing" frame situation
     * changed from the one before execute()ing.
     */
    boolean execute(Frame inFrame, ArrayList<InstructionContext> executionPredecessors,
            InstConstraintVisitor icv, ExecutionVisitor ev);

    Frame getInFrame();

    /**
     * This method returns the outgoing execution frame situation;
     * therefore <B>it has to be calculated by execute(Frame, ArrayList)
     * first.</B>
     *
     * @see #execute(Frame, ArrayList, InstConstraintVisitor, ExecutionVisitor)
     */
    Frame getOutFrame(ArrayList<InstructionContext> executionPredecessors);

    /**
     * Returns the InstructionHandle this InstructionContext is wrapped around.
     *
     * @return The InstructionHandle this InstructionContext is wrapped around.
     */
    InstructionHandle getInstruction();

    /**
     * Returns the usual control flow successors.
     * @see #getExceptionHandlers()
     */
    InstructionContext[] getSuccessors();

    /**
     * Returns the exception handlers that protect this instruction.
     * They are special control flow successors.
     */
    ExceptionHandler[] getExceptionHandlers();
}