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.generic;
019
020/**
021 * BranchHandle is returned by specialized InstructionList.append() whenever a BranchInstruction is appended. This is
022 * useful when the target of this instruction is not known at time of creation and must be set later via setTarget().
023 *
024 * @see InstructionHandle
025 * @see Instruction
026 * @see InstructionList
027 */
028public final class BranchHandle extends InstructionHandle {
029
030    /**
031     * Factory method.
032     */
033    static BranchHandle getBranchHandle(final BranchInstruction i) {
034        return new BranchHandle(i);
035    }
036
037    // This is also a cache in case the InstructionHandle#swapInstruction() method is used
038    // See BCEL-273
039    private BranchInstruction bi; // An alias in fact, but saves lots of casts
040
041    private BranchHandle(final BranchInstruction i) {
042        super(i);
043        bi = i;
044    }
045
046    /*
047     * Override InstructionHandle methods: delegate to branch instruction. Through this overriding all access to the private
048     * i_position field should be prevented.
049     */
050    @Override
051    public int getPosition() {
052        return bi.getPosition();
053    }
054
055    /**
056     * @return target of instruction.
057     */
058    public InstructionHandle getTarget() {
059        return bi.getTarget();
060    }
061
062    /**
063     * Set new contents. Old instruction is disposed and may not be used anymore.
064     */
065    @Override // This is only done in order to apply the additional type check; could be merged with super impl.
066    public void setInstruction(final Instruction i) { // TODO could be package-protected?
067        super.setInstruction(i);
068        if (!(i instanceof BranchInstruction)) {
069            throw new ClassGenException("Assigning " + i + " to branch handle which is not a branch instruction");
070        }
071        bi = (BranchInstruction) i;
072    }
073
074    @Override
075    void setPosition(final int pos) {
076        // Original code: i_position = bi.position = pos;
077        bi.setPosition(pos);
078        super.setPosition(pos);
079    }
080
081    /**
082     * Pass new target to instruction.
083     */
084    public void setTarget(final InstructionHandle ih) {
085        bi.setTarget(ih);
086    }
087
088    @Override
089    protected int updatePosition(final int offset, final int max_offset) {
090        final int x = bi.updatePosition(offset, max_offset);
091        super.setPosition(bi.getPosition());
092        return x;
093    }
094
095    /**
096     * Update target of instruction.
097     */
098    public void updateTarget(final InstructionHandle old_ih, final InstructionHandle new_ih) {
099        bi.updateTarget(old_ih, new_ih);
100    }
101}