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}