    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;
    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
    029 * in the constant pool of a class file. The classes keep closely to
    030 * the JVM specification.
    031 *
    032 * @version $Id: Constant.java 1829452 2018-04-18 14:17:34Z markt $
    033 */
    034public abstract class Constant implements Cloneable, Node {
    035
    036    private static BCELComparator bcelComparator = new BCELComparator() {
    037
    038        @Override
    039        public boolean equals( final Object o1, final Object o2 ) {
    040            final Constant THIS = (Constant) o1;
    041            final Constant THAT = (Constant) o2;
    042            return THIS.toString().equals(THAT.toString());
    043        }
    044
    045
    046        @Override
    047        public int hashCode( final Object o ) {
    048            final Constant THIS = (Constant) o;
    049            return THIS.toString().hashCode();
    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
    067    Constant(final byte tag) {
    068        this.tag = tag;
    069    }
    070
    071
    072    /**
    073     * Called by objects that are traversing the nodes of the tree implicitely
    074     * defined by the contents of a Java class. I.e., the hierarchy of methods,
    075     * fields, attributes, etc. spawns a tree of objects.
    076     *
    077     * @param v Visitor object
    078     */
    079    @Override
    080    public abstract void accept( Visitor v );
    081
    082
    083    public abstract void dump( DataOutputStream file ) throws IOException;
    084
    085
    086    /**
    087     * @return Tag of constant, i.e., its type. No setTag() method to avoid
    088     * confusion.
    089     */
    090    public final byte getTag() {
    091        return tag;
    092    }
    093
    094
    095    /**
    096     * @return String representation.
    097     */
    098    @Override
    099    public String toString() {
    100        return Const.getConstantName(tag) + "[" + tag + "]";
    101    }
    102
    103
    104    /**
    105     * @return deep copy of this constant
    106     */
    107    public Constant copy() {
    108        try {
    109            return (Constant) super.clone();
    110        } catch (final CloneNotSupportedException e) {
    111            // TODO should this throw?
    112        }
    113        return null;
    114    }
    115
    116
    117    @Override
    118    public Object clone() {
    119        try {
    120            return super.clone();
    121        } catch (final CloneNotSupportedException e) {
    122            throw new Error("Clone Not Supported"); // never happens
    123        }
    124    }
    125
    126
    127    /**
    128     * Read one constant from the given input, the type depends on a tag byte.
    129     *
    130     * @param dataInput Input stream
    131     * @return Constant object
    132     * @throws IOException if an I/O error occurs reading from the given {@code dataInput}.
    133     * @throws ClassFormatException if the next byte is not recognized
    134     * @since 6.0 made public
    135     */
    136    public static Constant readConstant(final DataInput dataInput) throws IOException, ClassFormatException {
    137        final byte b = dataInput.readByte(); // Read tag byte
    138        switch (b) {
    139        case Const.CONSTANT_Class:
    140            return new ConstantClass(dataInput);
    141        case Const.CONSTANT_Fieldref:
    142            return new ConstantFieldref(dataInput);
    143        case Const.CONSTANT_Methodref:
    144            return new ConstantMethodref(dataInput);
    145        case Const.CONSTANT_InterfaceMethodref:
    146            return new ConstantInterfaceMethodref(dataInput);
    147        case Const.CONSTANT_String:
    148            return new ConstantString(dataInput);
    149        case Const.CONSTANT_Integer:
    150            return new ConstantInteger(dataInput);
    151        case Const.CONSTANT_Float:
    152            return new ConstantFloat(dataInput);
    153        case Const.CONSTANT_Long:
    154            return new ConstantLong(dataInput);
    155        case Const.CONSTANT_Double:
    156            return new ConstantDouble(dataInput);
    157        case Const.CONSTANT_NameAndType:
    158            return new ConstantNameAndType(dataInput);
    159        case Const.CONSTANT_Utf8:
    160            return ConstantUtf8.getInstance(dataInput);
    161        case Const.CONSTANT_MethodHandle:
    162            return new ConstantMethodHandle(dataInput);
    163        case Const.CONSTANT_MethodType:
    164            return new ConstantMethodType(dataInput);
    165        case Const.CONSTANT_Dynamic:
    166            return new ConstantDynamic(dataInput);
    167        case Const.CONSTANT_InvokeDynamic:
    168            return new ConstantInvokeDynamic(dataInput);
    169        case Const.CONSTANT_Module:
    170            return new ConstantModule(dataInput);
    171        case Const.CONSTANT_Package:
    172            return new ConstantPackage(dataInput);
    173        default:
    174            throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
    175        }
    176    }
    177
    178    /**
    179     * @return Comparison strategy object
    180     */
    181    public static BCELComparator getComparator() {
    182        return bcelComparator;
    183    }
    184
    185
    186    /**
    187     * @param comparator Comparison strategy object
    188     */
    189    public static void setComparator( final BCELComparator comparator ) {
    190        bcelComparator = comparator;
    191    }
    192
    193
    194    /**
    195     * Return value as defined by given BCELComparator strategy.
    196     * By default two Constant objects are said to be equal when
    197     * the result of toString() is equal.
    198     *
    199     * @see java.lang.Object#equals(java.lang.Object)
    200     */
    201    @Override
    202    public boolean equals( final Object obj ) {
    203        return bcelComparator.equals(this, obj);
    204    }
    205
    206
    207    /**
    208     * Return value as defined by given BCELComparator strategy.
    209     * By default return the hashcode of the result of toString().
    210     *
    211     * @see java.lang.Object#hashCode()
    212     */
    213    @Override
    214    public int hashCode() {
    215        return bcelComparator.hashCode(this);
    216    }
    217}