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     * Constructs a Synthetic attribute.
049     *
050     * @param nameIndex    Index in constant pool to CONSTANT_Utf8, which should represent the string "Synthetic".
051     * @param length       JVM Specification: "The value of the attribute_length item must be zero.".
052     * @param bytes        Attribute contents.
053     * @param constantPool The constant pool this attribute is associated with.
054     * @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>
055     */
056    public Synthetic(final int nameIndex, final int length, final byte[] bytes, final ConstantPool constantPool) {
057        super(Const.ATTR_SYNTHETIC, nameIndex, Args.require0(length, "Synthetic attribute length"), constantPool);
058    }
059
060    /**
061     * Constructs object from input stream.
062     *
063     * @param nameIndex    Index in constant pool to CONSTANT_Utf8.
064     * @param length       JVM Specification: "The value of the attribute_length item must be zero.".
065     * @param input        Input stream.
066     * @param constantPool Array of constants.
067     * @throws IOException Thrown if an I/O error occurs.
068     * @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>
069     */
070    Synthetic(final int nameIndex, final int length, final DataInput input, final ConstantPool constantPool) throws IOException {
071        this(nameIndex, length, (byte[]) null, constantPool);
072    }
073
074    /**
075     * Initialize from another object. Note that both objects use the same references (shallow copy). Use copy() for a physical copy.
076     *
077     * @param c Source to copy.
078     */
079    public Synthetic(final Synthetic c) {
080        this(c.getNameIndex(), c.getLength(), c.getBytes(), c.getConstantPool());
081    }
082
083    /**
084     * 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,
085     * attributes, etc. spawns a tree of objects.
086     *
087     * @param v Visitor object.
088     */
089    @Override
090    public void accept(final Visitor v) {
091        v.visitSynthetic(this);
092    }
093
094    /**
095     * @return deep copy of this attribute.
096     */
097    @Override
098    public Attribute copy(final ConstantPool constantPool) {
099        final Synthetic c = (Synthetic) clone();
100        c.setConstantPool(constantPool);
101        return c;
102    }
103
104    /**
105     * Gets data bytes.
106     *
107     * @return data bytes.
108     */
109    public byte[] getBytes() {
110        return ArrayUtils.EMPTY_BYTE_ARRAY;
111    }
112
113    /**
114     * Sets data bytes.
115     *
116     * @param bytes data bytes.
117     */
118    public void setBytes(final byte[] bytes) {
119        if (bytes != null) {
120            Args.require0(bytes.length, "Deprecated attribute length");
121        }
122    }
123
124    /**
125     * @return String representation.
126     */
127    @Override
128    public String toString() {
129        return "Synthetic";
130    }
131}