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}