001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   https://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019
020package org.apache.bcel.classfile;
021
022import java.io.DataInput;
023import java.io.IOException;
024
025import org.apache.bcel.Const;
026import org.apache.bcel.util.Args;
027import org.apache.commons.lang3.ArrayUtils;
028
029/**
030 * This class is derived from <em>Attribute</em> and declares this class as 'synthetic', that is, it needs special handling. The JVM specification states "A
031 * class member that does not appear in the source code must be marked using a Synthetic attribute." It may appear in the ClassFile attribute table, a
032 * field_info table or a method_info table. This class is intended to be instantiated from the <em>Attribute.readAttribute()</em> method.
033 *
034 * <pre>
035 *
036 * Synthetic_attribute {
037 *     u2 attribute_name_index;
038 *     u4 attribute_length;
039 * }
040 * </pre>
041 *
042 * @see Attribute
043 * @see <a href="https://docs.oracle.com/javase/specs/jvms/se25/html/jvms-4.html#jvms-4.7.8">JVM Specification: The Synthetic Attribute</a>
044 */
045public final class Synthetic extends Attribute {
046
047    /**
048     * @param nameIndex    Index in constant pool to CONSTANT_Utf8, which should represent the string "Synthetic".
049     * @param length       JVM Specification: "The value of the attribute_length item must be zero.".
050     * @param bytes        Attribute contents.
051     * @param constantPool The constant pool this attribute is associated with.
052     * @see <a href="https://docs.oracle.com/javase/specs/jvms/se25/html/jvms-4.html#jvms-4.7.8">JVM Specification: The Synthetic Attribute</a>
053     */
054    public Synthetic(final int nameIndex, final int length, final byte[] bytes, final ConstantPool constantPool) {
055        super(Const.ATTR_SYNTHETIC, nameIndex, Args.require0(length, "Synthetic attribute length"), constantPool);
056    }
057
058    /**
059     * Constructs object from input stream.
060     *
061     * @param nameIndex    Index in constant pool to CONSTANT_Utf8.
062     * @param length       JVM Specification: "The value of the attribute_length item must be zero.".
063     * @param input        Input stream.
064     * @param constantPool Array of constants.
065     * @throws IOException if an I/O error occurs.
066     * @see <a href="https://docs.oracle.com/javase/specs/jvms/se25/html/jvms-4.html#jvms-4.7.8">JVM Specification: The Synthetic Attribute</a>
067     */
068    Synthetic(final int nameIndex, final int length, final DataInput input, final ConstantPool constantPool) throws IOException {
069        this(nameIndex, length, (byte[]) null, constantPool);
070    }
071
072    /**
073     * Initialize from another object. Note that both objects use the same references (shallow copy). Use copy() for a physical copy.
074     *
075     * @param c Source to copy.
076     */
077    public Synthetic(final Synthetic c) {
078        this(c.getNameIndex(), c.getLength(), c.getBytes(), c.getConstantPool());
079    }
080
081    /**
082     * 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,
083     * attributes, etc. spawns a tree of objects.
084     *
085     * @param v Visitor object.
086     */
087    @Override
088    public void accept(final Visitor v) {
089        v.visitSynthetic(this);
090    }
091
092    /**
093     * @return deep copy of this attribute.
094     */
095    @Override
096    public Attribute copy(final ConstantPool constantPool) {
097        final Synthetic c = (Synthetic) clone();
098        c.setConstantPool(constantPool);
099        return c;
100    }
101
102    /**
103     * Gets data bytes.
104     *
105     * @return data bytes.
106     */
107    public byte[] getBytes() {
108        return ArrayUtils.EMPTY_BYTE_ARRAY;
109    }
110
111    /**
112     * Sets data bytes.
113     *
114     * @param bytes data bytes.
115     */
116    public void setBytes(final byte[] bytes) {
117        if (bytes != null) {
118            Args.require0(bytes.length, "Deprecated attribute length");
119        }
120    }
121
122    /**
123     * @return String representation.
124     */
125    @Override
126    public String toString() {
127        return "Synthetic";
128    }
129}