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