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