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 * Licensed to the Apache Software Foundation (ASF) under one or more
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 * 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
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 * distributed under the License is distributed on an "AS IS" BASIS,
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package com.sun.org.apache.bcel.internal.classfile;

import java.io.DataInput;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.Objects;

import com.sun.org.apache.bcel.internal.Const;
import com.sun.org.apache.bcel.internal.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.
@LastModified: Jan 2020
/** * 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. * * @LastModified: Jan 2020 */
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(); } }; /* 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. */ private byte tag; Constant(final byte tag) { this.tag = tag; }
Called by objects that are traversing the nodes of the tree implicitely defined by the contents of a Java class. I.e., the hierarchy of methods, fields, attributes, etc. spawns a tree of objects.
Params:
  • v – Visitor object
/** * Called by objects that are traversing the nodes of the tree implicitely * 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 ); public abstract void dump( DataOutputStream file ) throws IOException;
Returns:Tag of constant, i.e., its type. No setTag() method to avoid confusion.
/** * @return Tag of constant, i.e., its type. No setTag() method to avoid * confusion. */
public final byte getTag() { return tag; }
Returns:String representation.
/** * @return String representation. */
@Override public String toString() { return Const.getConstantName(tag) + "[" + tag + "]"; }
Returns:deep copy of this constant
/** * @return deep copy of this constant */
public Constant copy() { try { return (Constant) super.clone(); } catch (final CloneNotSupportedException e) { // TODO should this throw? } return null; } @Override public Object clone() { try { return super.clone(); } catch (final CloneNotSupportedException e) { throw new Error("Clone Not Supported"); // never happens } }
Reads one constant from the given input, the type depends on a tag byte.
Params:
  • dataInput – Input stream
Throws:
Returns:Constant object
Since:6.0 made public
/** * 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); } }
Returns:Comparison strategy object
/** * @return Comparison strategy object */
public static BCELComparator getComparator() { return bcelComparator; }
Params:
  • comparator – Comparison strategy object
/** * @param comparator Comparison strategy object */
public static void setComparator( final BCELComparator comparator ) { bcelComparator = comparator; }
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 Also:
  • equals.equals(Object)
/** * 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 java.lang.Object#equals(java.lang.Object) */
@Override public boolean equals( final Object obj ) { return bcelComparator.equals(this, obj); }
Returns value as defined by given BCELComparator strategy. By default return the hashcode of the result of toString().
See Also:
  • hashCode.hashCode()
/** * Returns value as defined by given BCELComparator strategy. * By default return the hashcode of the result of toString(). * * @see java.lang.Object#hashCode() */
@Override public int hashCode() { return bcelComparator.hashCode(this); } }