1 /* 2 * Licensed to the Apache Software Foundation (ASF) under one or more 3 * contributor license agreements. See the NOTICE file distributed with 4 * this work for additional information regarding copyright ownership. 5 * The ASF licenses this file to You under the Apache License, Version 2.0 6 * (the "License"); you may not use this file except in compliance with 7 * the License. You may obtain a copy of the License at 8 * 9 * http://www.apache.org/licenses/LICENSE-2.0 10 * 11 * Unless required by applicable law or agreed to in writing, software 12 * distributed under the License is distributed on an "AS IS" BASIS, 13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 14 * See the License for the specific language governing permissions and 15 * limitations under the License. 16 * 17 */ 18 package org.apache.bcel.classfile; 19 20 import java.io.DataInput; 21 import java.io.DataOutputStream; 22 import java.io.IOException; 23 24 import org.apache.bcel.Const; 25 import org.apache.bcel.util.BCELComparator; 26 27 /** 28 * Abstract superclass for classes to represent the different constant types 29 * in the constant pool of a class file. The classes keep closely to 30 * the JVM specification. 31 * 32 * @version $Id$ 33 */ 34 public abstract class Constant implements Cloneable, Node { 35 36 private static BCELComparator bcelComparator = new BCELComparator() { 37 38 @Override 39 public boolean equals( final Object o1, final Object o2 ) { 40 final Constant THIS = (Constant) o1; 41 final Constant THAT = (Constant) o2; 42 return THIS.toString().equals(THAT.toString()); 43 } 44 45 46 @Override 47 public int hashCode( final Object o ) { 48 final Constant THIS = (Constant) o; 49 return THIS.toString().hashCode(); 50 } 51 }; 52 /* In fact this tag is redundant since we can distinguish different 53 * `Constant' objects by their type, i.e., via `instanceof'. In some 54 * places we will use the tag for switch()es anyway. 55 * 56 * First, we want match the specification as closely as possible. Second we 57 * need the tag as an index to select the corresponding class name from the 58 * `CONSTANT_NAMES' array. 59 */ 60 /** 61 * @deprecated (since 6.0) will be made private; do not access directly, use getter/setter 62 */ 63 @java.lang.Deprecated 64 protected byte tag; // TODO should be private & final 65 66 67 Constant(final byte tag) { 68 this.tag = tag; 69 } 70 71 72 /** 73 * Called by objects that are traversing the nodes of the tree implicitely 74 * defined by the contents of a Java class. I.e., the hierarchy of methods, 75 * fields, attributes, etc. spawns a tree of objects. 76 * 77 * @param v Visitor object 78 */ 79 @Override 80 public abstract void accept( Visitor v ); 81 82 83 public abstract void dump( DataOutputStream file ) throws IOException; 84 85 86 /** 87 * @return Tag of constant, i.e., its type. No setTag() method to avoid 88 * confusion. 89 */ 90 public final byte getTag() { 91 return tag; 92 } 93 94 95 /** 96 * @return String representation. 97 */ 98 @Override 99 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 input Input stream 131 * @return Constant object 132 * @since 6.0 made public 133 */ 134 public static Constant readConstant( final DataInput input ) throws IOException, 135 ClassFormatException { 136 final byte b = input.readByte(); // Read tag byte 137 switch (b) { 138 case Const.CONSTANT_Class: 139 return new ConstantClass(input); 140 case Const.CONSTANT_Fieldref: 141 return new ConstantFieldref(input); 142 case Const.CONSTANT_Methodref: 143 return new ConstantMethodref(input); 144 case Const.CONSTANT_InterfaceMethodref: 145 return new ConstantInterfaceMethodref(input); 146 case Const.CONSTANT_String: 147 return new ConstantString(input); 148 case Const.CONSTANT_Integer: 149 return new ConstantInteger(input); 150 case Const.CONSTANT_Float: 151 return new ConstantFloat(input); 152 case Const.CONSTANT_Long: 153 return new ConstantLong(input); 154 case Const.CONSTANT_Double: 155 return new ConstantDouble(input); 156 case Const.CONSTANT_NameAndType: 157 return new ConstantNameAndType(input); 158 case Const.CONSTANT_Utf8: 159 return ConstantUtf8.getInstance(input); 160 case Const.CONSTANT_MethodHandle: 161 return new ConstantMethodHandle(input); 162 case Const.CONSTANT_MethodType: 163 return new ConstantMethodType(input); 164 case Const.CONSTANT_InvokeDynamic: 165 return new ConstantInvokeDynamic(input); 166 case Const.CONSTANT_Module: 167 return new ConstantModule(input); 168 case Const.CONSTANT_Package: 169 return new ConstantPackage(input); 170 default: 171 throw new ClassFormatException("Invalid byte tag in constant pool: " + b); 172 } 173 } 174 175 176 /** 177 * @return Comparison strategy object 178 */ 179 public static BCELComparator getComparator() { 180 return bcelComparator; 181 } 182 183 184 /** 185 * @param comparator Comparison strategy object 186 */ 187 public static void setComparator( final BCELComparator comparator ) { 188 bcelComparator = comparator; 189 } 190 191 192 /** 193 * Return value as defined by given BCELComparator strategy. 194 * By default two Constant objects are said to be equal when 195 * the result of toString() is equal. 196 * 197 * @see java.lang.Object#equals(java.lang.Object) 198 */ 199 @Override 200 public boolean equals( final Object obj ) { 201 return bcelComparator.equals(this, obj); 202 } 203 204 205 /** 206 * Return value as defined by given BCELComparator strategy. 207 * By default return the hashcode of the result of toString(). 208 * 209 * @see java.lang.Object#hashCode() 210 */ 211 @Override 212 public int hashCode() { 213 return bcelComparator.hashCode(this); 214 } 215 } 216