Constant.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.bcel.classfile;
import java.io.DataInput;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.Objects;
import org.apache.bcel.Const;
import org.apache.bcel.util.BCELComparator;
/**
* Abstract superclass for classes to represent the different constant types in the constant pool of a class file. The
* classes keep closely to the JVM specification.
*/
public abstract class Constant implements Cloneable, Node {
private static BCELComparator bcelComparator = new BCELComparator() {
@Override
public boolean equals(final Object o1, final Object o2) {
final Constant THIS = (Constant) o1;
final Constant THAT = (Constant) o2;
return Objects.equals(THIS.toString(), THAT.toString());
}
@Override
public int hashCode(final Object o) {
final Constant THIS = (Constant) o;
return THIS.toString().hashCode();
}
};
/**
* @return Comparison strategy object
*/
public static BCELComparator getComparator() {
return bcelComparator;
}
/**
* Reads one constant from the given input, the type depends on a tag byte.
*
* @param dataInput Input stream
* @return Constant object
* @throws IOException if an I/O error occurs reading from the given {@code dataInput}.
* @throws ClassFormatException if the next byte is not recognized
* @since 6.0 made public
*/
public static Constant readConstant(final DataInput dataInput) throws IOException, ClassFormatException {
final byte b = dataInput.readByte(); // Read tag byte
switch (b) {
case Const.CONSTANT_Class:
return new ConstantClass(dataInput);
case Const.CONSTANT_Fieldref:
return new ConstantFieldref(dataInput);
case Const.CONSTANT_Methodref:
return new ConstantMethodref(dataInput);
case Const.CONSTANT_InterfaceMethodref:
return new ConstantInterfaceMethodref(dataInput);
case Const.CONSTANT_String:
return new ConstantString(dataInput);
case Const.CONSTANT_Integer:
return new ConstantInteger(dataInput);
case Const.CONSTANT_Float:
return new ConstantFloat(dataInput);
case Const.CONSTANT_Long:
return new ConstantLong(dataInput);
case Const.CONSTANT_Double:
return new ConstantDouble(dataInput);
case Const.CONSTANT_NameAndType:
return new ConstantNameAndType(dataInput);
case Const.CONSTANT_Utf8:
return ConstantUtf8.getInstance(dataInput);
case Const.CONSTANT_MethodHandle:
return new ConstantMethodHandle(dataInput);
case Const.CONSTANT_MethodType:
return new ConstantMethodType(dataInput);
case Const.CONSTANT_Dynamic:
return new ConstantDynamic(dataInput);
case Const.CONSTANT_InvokeDynamic:
return new ConstantInvokeDynamic(dataInput);
case Const.CONSTANT_Module:
return new ConstantModule(dataInput);
case Const.CONSTANT_Package:
return new ConstantPackage(dataInput);
default:
throw new ClassFormatException("Invalid byte tag in constant pool: " + b);
}
}
/**
* @param comparator Comparison strategy object
*/
public static void setComparator(final BCELComparator comparator) {
bcelComparator = comparator;
}
/*
* In fact this tag is redundant since we can distinguish different 'Constant' objects by their type, i.e., via
* 'instanceof'. In some places we will use the tag for switch()es anyway.
*
* First, we want match the specification as closely as possible. Second we need the tag as an index to select the
* corresponding class name from the 'CONSTANT_NAMES' array.
*/
/**
* @deprecated (since 6.0) will be made private; do not access directly, use getter/setter
*/
@java.lang.Deprecated
protected byte tag; // TODO should be private & final
Constant(final byte tag) {
this.tag = tag;
}
/**
* Called by objects that are traversing the nodes of the tree implicitly defined by the contents of a Java class.
* I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
*
* @param v Visitor object
*/
@Override
public abstract void accept(Visitor v);
@Override
public Object clone() {
try {
return super.clone();
} catch (final CloneNotSupportedException e) {
throw new UnsupportedOperationException("Clone Not Supported", e); // never happens
}
}
/**
* @return deep copy of this constant
*/
public Constant copy() {
try {
return (Constant) super.clone();
} catch (final CloneNotSupportedException e) {
// TODO should this throw?
}
return null;
}
public abstract void dump(DataOutputStream file) throws IOException;
/**
* Returns value as defined by given BCELComparator strategy. By default two Constant objects are said to be equal when
* the result of toString() is equal.
*
* @see Object#equals(Object)
*/
@Override
public boolean equals(final Object obj) {
return bcelComparator.equals(this, obj);
}
/**
* @return Tag of constant, i.e., its type. No setTag() method to avoid confusion.
*/
public final byte getTag() {
return tag;
}
/**
* Returns value as defined by given BCELComparator strategy. By default return the hash code of the result of
* toString().
*
* @see Object#hashCode()
*/
@Override
public int hashCode() {
return bcelComparator.hashCode(this);
}
/**
* @return String representation.
*/
@Override
public String toString() {
return Const.getConstantName(tag) + "[" + tag + "]";
}
}