    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 *
    033 * @version $Id$
    034 */
    035public abstract class Constant implements Cloneable, Node {
    036
    037    private static BCELComparator bcelComparator = new BCELComparator() {
    038
    039        @Override
    040        public boolean equals( final Object o1, final Object o2 ) {
    041            final Constant THIS = (Constant) o1;
    042            final Constant THAT = (Constant) o2;
    043            return Objects.equals(THIS.toString(), THAT.toString());
    044        }
    045
    046
    047        @Override
    048        public int hashCode( final Object o ) {
    049            final Constant THIS = (Constant) o;
    050            return THIS.toString().hashCode();
    051        }
    052    };
    053    /* In fact this tag is redundant since we can distinguish different
    054     * `Constant' objects by their type, i.e., via `instanceof'. In some
    055     * places we will use the tag for switch()es anyway.
    056     *
    057     * First, we want match the specification as closely as possible. Second we
    058     * need the tag as an index to select the corresponding class name from the
    059     * `CONSTANT_NAMES' array.
    060     */
    061    /**
    062     * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
    063     */
    064    @java.lang.Deprecated
    065    protected byte tag; // TODO should be private & final
    066
    067
    068    Constant(final byte tag) {
    069        this.tag = tag;
    070    }
    071
    072
    073    /**
    074     * Called by objects that are traversing the nodes of the tree implicitely
    075     * defined by the contents of a Java class. I.e., the hierarchy of methods,
    076     * fields, attributes, etc. spawns a tree of objects.
    077     *
    078     * @param v Visitor object
    079     */
    080    @Override
    081    public abstract void accept( Visitor v );
    082
    083
    084    public abstract void dump( DataOutputStream file ) throws IOException;
    085
    086
    087    /**
    088     * @return Tag of constant, i.e., its type. No setTag() method to avoid
    089     * confusion.
    090     */
    091    public final byte getTag() {
    092        return tag;
    093    }
    094
    095
    096    /**
    097     * @return String representation.
    098     */
    099    @Override
    100    public String toString() {
    101        return Const.getConstantName(tag) + "[" + tag + "]";
    102    }
    103
    104
    105    /**
    106     * @return deep copy of this constant
    107     */
    108    public Constant copy() {
    109        try {
    110            return (Constant) super.clone();
    111        } catch (final CloneNotSupportedException e) {
    112            // TODO should this throw?
    113        }
    114        return null;
    115    }
    116
    117
    118    @Override
    119    public Object clone() {
    120        try {
    121            return super.clone();
    122        } catch (final CloneNotSupportedException e) {
    123            throw new Error("Clone Not Supported"); // never happens
    124        }
    125    }
    126
    127
    128    /**
    129     * Read one constant from the given input, the type depends on a tag byte.
    130     *
    131     * @param dataInput Input stream
    132     * @return Constant object
    133     * @throws IOException if an I/O error occurs reading from the given {@code dataInput}.
    134     * @throws ClassFormatException if the next byte is not recognized
    135     * @since 6.0 made public
    136     */
    137    public static Constant readConstant(final DataInput dataInput) throws IOException, ClassFormatException {
    138        final byte b = dataInput.readByte(); // Read tag byte
    139        switch (b) {
    140        case Const.CONSTANT_Class:
    141            return new ConstantClass(dataInput);
    142        case Const.CONSTANT_Fieldref:
    143            return new ConstantFieldref(dataInput);
    144        case Const.CONSTANT_Methodref:
    145            return new ConstantMethodref(dataInput);
    146        case Const.CONSTANT_InterfaceMethodref:
    147            return new ConstantInterfaceMethodref(dataInput);
    148        case Const.CONSTANT_String:
    149            return new ConstantString(dataInput);
    150        case Const.CONSTANT_Integer:
    151            return new ConstantInteger(dataInput);
    152        case Const.CONSTANT_Float:
    153            return new ConstantFloat(dataInput);
    154        case Const.CONSTANT_Long:
    155            return new ConstantLong(dataInput);
    156        case Const.CONSTANT_Double:
    157            return new ConstantDouble(dataInput);
    158        case Const.CONSTANT_NameAndType:
    159            return new ConstantNameAndType(dataInput);
    160        case Const.CONSTANT_Utf8:
    161            return ConstantUtf8.getInstance(dataInput);
    162        case Const.CONSTANT_MethodHandle:
    163            return new ConstantMethodHandle(dataInput);
    164        case Const.CONSTANT_MethodType:
    165            return new ConstantMethodType(dataInput);
    166        case Const.CONSTANT_Dynamic:
    167            return new ConstantDynamic(dataInput);
    168        case Const.CONSTANT_InvokeDynamic:
    169            return new ConstantInvokeDynamic(dataInput);
    170        case Const.CONSTANT_Module:
    171            return new ConstantModule(dataInput);
    172        case Const.CONSTANT_Package:
    173            return new ConstantPackage(dataInput);
    174        default:
    175            throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
    176        }
    177    }
    178
    179    /**
    180     * @return Comparison strategy object
    181     */
    182    public static BCELComparator getComparator() {
    183        return bcelComparator;
    184    }
    185
    186
    187    /**
    188     * @param comparator Comparison strategy object
    189     */
    190    public static void setComparator( final BCELComparator comparator ) {
    191        bcelComparator = comparator;
    192    }
    193
    194
    195    /**
    196     * Return value as defined by given BCELComparator strategy.
    197     * By default two Constant objects are said to be equal when
    198     * the result of toString() is equal.
    199     *
    200     * @see java.lang.Object#equals(java.lang.Object)
    201     */
    202    @Override
    203    public boolean equals( final Object obj ) {
    204        return bcelComparator.equals(this, obj);
    205    }
    206
    207
    208    /**
    209     * Return value as defined by given BCELComparator strategy.
    210     * By default return the hashcode of the result of toString().
    211     *
    212     * @see java.lang.Object#hashCode()
    213     */
    214    @Override
    215    public int hashCode() {
    216        return bcelComparator.hashCode(this);
    217    }
    218}