    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.classfile;
    019
    020import java.io.DataInput;
    021import java.io.DataOutputStream;
    022import java.io.IOException;
    023import java.util.Objects;
    024
    025import org.apache.bcel.Const;
    026import org.apache.bcel.util.BCELComparator;
    027
    028/**
    029 * Abstract superclass for classes to represent the different constant types
    030 * in the constant pool of a class file. The classes keep closely to
    031 * the JVM specification.
    032 */
    033public abstract class Constant implements Cloneable, Node {
    034
    035    private static BCELComparator bcelComparator = new BCELComparator() {
    036
    037        @Override
    038        public boolean equals( final Object o1, final Object o2 ) {
    039            final Constant THIS = (Constant) o1;
    040            final Constant THAT = (Constant) o2;
    041            return Objects.equals(THIS.toString(), THAT.toString());
    042        }
    043
    044
    045        @Override
    046        public int hashCode( final Object o ) {
    047            final Constant THIS = (Constant) o;
    048            return THIS.toString().hashCode();
    049        }
    050    };
    051
    052    /* In fact this tag is redundant since we can distinguish different
    053     * `Constant' objects by their type, i.e., via `instanceof'. In some
    054     * places we will use the tag for switch()es anyway.
    055     *
    056     * First, we want match the specification as closely as possible. Second we
    057     * need the tag as an index to select the corresponding class name from the
    058     * `CONSTANT_NAMES' array.
    059     */
    060    /**
    061     * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
    062     */
    063    @java.lang.Deprecated
    064    protected byte tag; // TODO should be private & final
    065
    066    Constant(final byte tag) {
    067        this.tag = tag;
    068    }
    069
    070    /**
    071     * Called by objects that are traversing the nodes of the tree implicitely
    072     * defined by the contents of a Java class. I.e., the hierarchy of methods,
    073     * fields, attributes, etc. spawns a tree of objects.
    074     *
    075     * @param v Visitor object
    076     */
    077    @Override
    078    public abstract void accept( Visitor v );
    079
    080    public abstract void dump( DataOutputStream file ) throws IOException;
    081
    082    /**
    083     * @return Tag of constant, i.e., its type. No setTag() method to avoid
    084     * confusion.
    085     */
    086    public final byte getTag() {
    087        return tag;
    088    }
    089
    090    /**
    091     * @return String representation.
    092     */
    093    @Override
    094    public String toString() {
    095        return Const.getConstantName(tag) + "[" + tag + "]";
    096    }
    097
    098    /**
    099     * @return deep copy of this constant
    100     */
    101    public Constant copy() {
    102        try {
    103            return (Constant) super.clone();
    104        } catch (final CloneNotSupportedException e) {
    105            // TODO should this throw?
    106        }
    107        return null;
    108    }
    109
    110    @Override
    111    public Object clone() {
    112        try {
    113            return super.clone();
    114        } catch (final CloneNotSupportedException e) {
    115            throw new Error("Clone Not Supported"); // never happens
    116        }
    117    }
    118
    119    /**
    120     * Reads one constant from the given input, the type depends on a tag byte.
    121     *
    122     * @param dataInput Input stream
    123     * @return Constant object
    124     * @throws IOException if an I/O error occurs reading from the given {@code dataInput}.
    125     * @throws ClassFormatException if the next byte is not recognized
    126     * @since 6.0 made public
    127     */
    128    public static Constant readConstant(final DataInput dataInput) throws IOException, ClassFormatException {
    129        final byte b = dataInput.readByte(); // Read tag byte
    130        switch (b) {
    131        case Const.CONSTANT_Class:
    132            return new ConstantClass(dataInput);
    133        case Const.CONSTANT_Fieldref:
    134            return new ConstantFieldref(dataInput);
    135        case Const.CONSTANT_Methodref:
    136            return new ConstantMethodref(dataInput);
    137        case Const.CONSTANT_InterfaceMethodref:
    138            return new ConstantInterfaceMethodref(dataInput);
    139        case Const.CONSTANT_String:
    140            return new ConstantString(dataInput);
    141        case Const.CONSTANT_Integer:
    142            return new ConstantInteger(dataInput);
    143        case Const.CONSTANT_Float:
    144            return new ConstantFloat(dataInput);
    145        case Const.CONSTANT_Long:
    146            return new ConstantLong(dataInput);
    147        case Const.CONSTANT_Double:
    148            return new ConstantDouble(dataInput);
    149        case Const.CONSTANT_NameAndType:
    150            return new ConstantNameAndType(dataInput);
    151        case Const.CONSTANT_Utf8:
    152            return ConstantUtf8.getInstance(dataInput);
    153        case Const.CONSTANT_MethodHandle:
    154            return new ConstantMethodHandle(dataInput);
    155        case Const.CONSTANT_MethodType:
    156            return new ConstantMethodType(dataInput);
    157        case Const.CONSTANT_Dynamic:
    158            return new ConstantDynamic(dataInput);
    159        case Const.CONSTANT_InvokeDynamic:
    160            return new ConstantInvokeDynamic(dataInput);
    161        case Const.CONSTANT_Module:
    162            return new ConstantModule(dataInput);
    163        case Const.CONSTANT_Package:
    164            return new ConstantPackage(dataInput);
    165        default:
    166            throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
    167        }
    168    }
    169
    170    /**
    171     * @return Comparison strategy object
    172     */
    173    public static BCELComparator getComparator() {
    174        return bcelComparator;
    175    }
    176
    177    /**
    178     * @param comparator Comparison strategy object
    179     */
    180    public static void setComparator( final BCELComparator comparator ) {
    181        bcelComparator = comparator;
    182    }
    183
    184    /**
    185     * Returns value as defined by given BCELComparator strategy.
    186     * By default two Constant objects are said to be equal when
    187     * the result of toString() is equal.
    188     *
    189     * @see java.lang.Object#equals(java.lang.Object)
    190     */
    191    @Override
    192    public boolean equals( final Object obj ) {
    193        return bcelComparator.equals(this, obj);
    194    }
    195
    196    /**
    197     * Returns value as defined by given BCELComparator strategy.
    198     * By default return the hashcode of the result of toString().
    199     *
    200     * @see java.lang.Object#hashCode()
    201     */
    202    @Override
    203    public int hashCode() {
    204        return bcelComparator.hashCode(this);
    205    }
    206}