    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 */
    017package org.apache.bcel.classfile;
    018
    019import java.io.DataInput;
    020import java.io.DataOutputStream;
    021import java.io.IOException;
    022import java.util.Objects;
    023
    024import org.apache.bcel.Const;
    025import org.apache.bcel.util.BCELComparator;
    026
    027/**
    028 * Abstract superclass for classes to represent the different constant types in the constant pool of a class file. The
    029 * classes keep closely to the JVM specification.
    030 */
    031public abstract class Constant implements Cloneable, Node {
    032
    033    static final Constant[] EMPTY_ARRAY = {};
    034
    035    private static BCELComparator<Constant> bcelComparator = new BCELComparator<Constant>() {
    036
    037        @Override
    038        public boolean equals(final Constant a, final Constant b) {
    039            return a == b || a != null && b != null && Objects.equals(a.toString(), b.toString());
    040        }
    041
    042        @Override
    043        public int hashCode(final Constant o) {
    044            return o != null ? Objects.hashCode(o.toString()) : 0;
    045        }
    046    };
    047
    048    /**
    049     * @return Comparison strategy object.
    050     */
    051    public static BCELComparator<Constant> getComparator() {
    052        return bcelComparator;
    053    }
    054
    055    /**
    056     * Reads one constant from the given input, the type depends on a tag byte.
    057     *
    058     * @param dataInput Input stream
    059     * @return Constant object
    060     * @throws IOException if an I/O error occurs reading from the given {@code dataInput}.
    061     * @throws ClassFormatException if the next byte is not recognized
    062     * @since 6.0 made public
    063     */
    064    public static Constant readConstant(final DataInput dataInput) throws IOException, ClassFormatException {
    065        final byte b = dataInput.readByte(); // Read tag byte
    066        switch (b) {
    067        case Const.CONSTANT_Class:
    068            return new ConstantClass(dataInput);
    069        case Const.CONSTANT_Fieldref:
    070            return new ConstantFieldref(dataInput);
    071        case Const.CONSTANT_Methodref:
    072            return new ConstantMethodref(dataInput);
    073        case Const.CONSTANT_InterfaceMethodref:
    074            return new ConstantInterfaceMethodref(dataInput);
    075        case Const.CONSTANT_String:
    076            return new ConstantString(dataInput);
    077        case Const.CONSTANT_Integer:
    078            return new ConstantInteger(dataInput);
    079        case Const.CONSTANT_Float:
    080            return new ConstantFloat(dataInput);
    081        case Const.CONSTANT_Long:
    082            return new ConstantLong(dataInput);
    083        case Const.CONSTANT_Double:
    084            return new ConstantDouble(dataInput);
    085        case Const.CONSTANT_NameAndType:
    086            return new ConstantNameAndType(dataInput);
    087        case Const.CONSTANT_Utf8:
    088            return ConstantUtf8.getInstance(dataInput);
    089        case Const.CONSTANT_MethodHandle:
    090            return new ConstantMethodHandle(dataInput);
    091        case Const.CONSTANT_MethodType:
    092            return new ConstantMethodType(dataInput);
    093        case Const.CONSTANT_Dynamic:
    094            return new ConstantDynamic(dataInput);
    095        case Const.CONSTANT_InvokeDynamic:
    096            return new ConstantInvokeDynamic(dataInput);
    097        case Const.CONSTANT_Module:
    098            return new ConstantModule(dataInput);
    099        case Const.CONSTANT_Package:
    100            return new ConstantPackage(dataInput);
    101        default:
    102            throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
    103        }
    104    }
    105
    106    /**
    107     * @param comparator Comparison strategy object
    108     */
    109    public static void setComparator(final BCELComparator<Constant> comparator) {
    110        bcelComparator = comparator;
    111    }
    112
    113    /*
    114     * In fact this tag is redundant since we can distinguish different 'Constant' objects by their type, i.e., via
    115     * 'instanceof'. In some places we will use the tag for switch()es anyway.
    116     *
    117     * First, we want match the specification as closely as possible. Second we need the tag as an index to select the
    118     * corresponding class name from the 'CONSTANT_NAMES' array.
    119     */
    120    /**
    121     * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
    122     */
    123    @java.lang.Deprecated
    124    protected byte tag; // TODO should be private & final
    125
    126    Constant(final byte tag) {
    127        this.tag = tag;
    128    }
    129
    130    /**
    131     * Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
    132     * I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
    133     *
    134     * @param v Visitor object
    135     */
    136    @Override
    137    public abstract void accept(Visitor v);
    138
    139    @Override
    140    public Object clone() {
    141        try {
    142            return super.clone();
    143        } catch (final CloneNotSupportedException e) {
    144            throw new UnsupportedOperationException("Clone Not Supported", e); // never happens
    145        }
    146    }
    147
    148    /**
    149     * @return deep copy of this constant
    150     */
    151    public Constant copy() {
    152        try {
    153            return (Constant) super.clone();
    154        } catch (final CloneNotSupportedException e) {
    155            // TODO should this throw?
    156        }
    157        return null;
    158    }
    159
    160    public abstract void dump(DataOutputStream file) throws IOException;
    161
    162    /**
    163     * Returns value as defined by given BCELComparator strategy. By default two Constant objects are said to be equal when
    164     * the result of toString() is equal.
    165     *
    166     * @see Object#equals(Object)
    167     */
    168    @Override
    169    public boolean equals(final Object obj) {
    170        return obj instanceof Constant && bcelComparator.equals(this, (Constant) obj);
    171    }
    172
    173    /**
    174     * @return Tag of constant, i.e., its type. No setTag() method to avoid confusion.
    175     */
    176    public final byte getTag() {
    177        return tag;
    178    }
    179
    180    /**
    181     * Returns value as defined by given BCELComparator strategy. By default return the hash code of the result of
    182     * toString().
    183     *
    184     * @see Object#hashCode()
    185     */
    186    @Override
    187    public int hashCode() {
    188        return bcelComparator.hashCode(this);
    189    }
    190
    191    /**
    192     * @return String representation.
    193     */
    194    @Override
    195    public String toString() {
    196        return Const.getConstantName(tag) + "[" + tag + "]";
    197    }
    198}