    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
    022 * BranchInstruction is appended. This is useful when the target of this
    023 * instruction is not known at time of creation and must be set later
    024 * via setTarget().
    025 *
    026 * @see InstructionHandle
    027 * @see Instruction
    028 * @see InstructionList
    029 * @version $Id: BranchHandle.java 1806200 2017-08-25 16:33:06Z ggregory $
    030 */
    031public final class BranchHandle extends InstructionHandle {
    032
    033    // This is also a cache in case the InstructionHandle#swapInstruction() method is used
    034    // See BCEL-273
    035    private BranchInstruction bi; // An alias in fact, but saves lots of casts
    036
    037
    038    private BranchHandle(final BranchInstruction i) {
    039        super(i);
    040        bi = i;
    041    }
    042
    043    /** Factory methods.
    044     */
    045    private static BranchHandle bh_list = null; // List of reusable handles
    046
    047
    048    static BranchHandle getBranchHandle( final BranchInstruction i ) {
    049        if (bh_list == null) {
    050            return new BranchHandle(i);
    051        }
    052        final BranchHandle bh = bh_list;
    053        bh_list = (BranchHandle) bh.getNext();
    054        bh.setInstruction(i);
    055        return bh;
    056    }
    057
    058
    059    /** Handle adds itself to the list of resuable handles.
    060     */
    061    @Override
    062    protected void addHandle() {
    063        super.setNext(bh_list);
    064        bh_list = this;
    065    }
    066
    067
    068    /* Override InstructionHandle methods: delegate to branch instruction.
    069     * Through this overriding all access to the private i_position field should
    070     * be prevented.
    071     */
    072    @Override
    073    public int getPosition() {
    074        return bi.getPosition();
    075    }
    076
    077
    078    @Override
    079    void setPosition( final int pos ) {
    080        // Original code: i_position = bi.position = pos;
    081        bi.setPosition(pos);
    082        super.setPosition(pos);
    083    }
    084
    085
    086    @Override
    087    protected int updatePosition( final int offset, final int max_offset ) {
    088        final int x = bi.updatePosition(offset, max_offset);
    089        super.setPosition(bi.getPosition());
    090        return x;
    091    }
    092
    093
    094    /**
    095     * Pass new target to instruction.
    096     */
    097    public void setTarget( final InstructionHandle ih ) {
    098        bi.setTarget(ih);
    099    }
    100
    101
    102    /**
    103     * Update target of instruction.
    104     */
    105    public void updateTarget( final InstructionHandle old_ih, final InstructionHandle new_ih ) {
    106        bi.updateTarget(old_ih, new_ih);
    107    }
    108
    109
    110    /**
    111     * @return target of instruction.
    112     */
    113    public InstructionHandle getTarget() {
    114        return bi.getTarget();
    115    }
    116
    117
    118    /**
    119     * Set new contents. Old instruction is disposed and may not be used anymore.
    120     */
    121    @Override // This is only done in order to apply the additional type check; could be merged with super impl.
    122    public void setInstruction( final Instruction i ) { // TODO could be package-protected?
    123        super.setInstruction(i);
    124        if (!(i instanceof BranchInstruction)) {
    125            throw new ClassGenException("Assigning " + i
    126                    + " to branch handle which is not a branch instruction");
    127        }
    128        bi = (BranchInstruction) i;
    129    }
    130}