src/main/java/org/apache/bcel/classfile/Synthetic.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
 *
 *   https://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.IOException;

import org.apache.bcel.Const;
import org.apache.bcel.util.Args;
import org.apache.commons.lang3.ArrayUtils;

/**
 * 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
 * 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
 * field_info table or a method_info table. This class is intended to be instantiated from the <em>Attribute.readAttribute()</em> method.
 *
 * <pre>
 *
 * Synthetic_attribute {
 *     u2 attribute_name_index;
 *     u4 attribute_length;
 * }
 * </pre>
 *
 * @see Attribute
 * @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>
 */
public final class Synthetic extends Attribute {

    /**
     * @param nameIndex    Index in constant pool to CONSTANT_Utf8, which should represent the string "Synthetic".
     * @param length       JVM Specification: "The value of the attribute_length item must be zero.".
     * @param bytes        Attribute contents.
     * @param constantPool The constant pool this attribute is associated with.
     * @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>
     */
    public Synthetic(final int nameIndex, final int length, final byte[] bytes, final ConstantPool constantPool) {
        super(Const.ATTR_SYNTHETIC, nameIndex, Args.require0(length, "Synthetic attribute length"), constantPool);
    }

    /**
     * Constructs object from input stream.
     *
     * @param nameIndex    Index in constant pool to CONSTANT_Utf8.
     * @param length       JVM Specification: "The value of the attribute_length item must be zero.".
     * @param input        Input stream.
     * @param constantPool Array of constants.
     * @throws IOException if an I/O error occurs.
     * @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>
     */
    Synthetic(final int nameIndex, final int length, final DataInput input, final ConstantPool constantPool) throws IOException {
        this(nameIndex, length, (byte[]) null, constantPool);
    }

    /**
     * Initialize from another object. Note that both objects use the same references (shallow copy). Use copy() for a physical copy.
     *
     * @param c Source to copy.
     */
    public Synthetic(final Synthetic c) {
        this(c.getNameIndex(), c.getLength(), c.getBytes(), c.getConstantPool());
    }

    /**
     * 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 void accept(final Visitor v) {
        v.visitSynthetic(this);
    }

    /**
     * @return deep copy of this attribute.
     */
    @Override
    public Attribute copy(final ConstantPool constantPool) {
        final Synthetic c = (Synthetic) clone();
        c.setConstantPool(constantPool);
        return c;
    }

    /**
     * Gets data bytes.
     *
     * @return data bytes.
     */
    public byte[] getBytes() {
        return ArrayUtils.EMPTY_BYTE_ARRAY;
    }

    /**
     * Sets data bytes.
     *
     * @param bytes data bytes.
     */
    public void setBytes(final byte[] bytes) {
        if (bytes != null) {
            Args.require0(bytes.length, "Deprecated attribute length");
        }
    }

    /**
     * @return String representation.
     */
    @Override
    public String toString() {
        return "Synthetic";
    }
}