src/java.base/share/classes/java/lang/classfile/constantpool/Utf8Entry.java

/*
 * Copyright (c) 2022, 2025, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */
package java.lang.classfile.constantpool;

import java.io.DataInput;
import java.lang.classfile.AnnotationValue;
import java.lang.classfile.MethodModel;
import java.lang.constant.ClassDesc;
import java.lang.constant.MethodTypeDesc;
import java.lang.invoke.TypeDescriptor;

import jdk.internal.classfile.impl.AbstractPoolEntry;

/**
 * Models a {@code CONSTANT_UTF8_info} constant, representing strings, in the
 * constant pool of a {@code class} file.  This describes strings in the
 * {@linkplain DataInput##modified-utf-8 Modified UTF-8} format.
 * <p>
 * The use of a {@code Utf8Entry} is represented by a {@link String}.
 * Conversions are through {@link ConstantPoolBuilder#utf8Entry(String)} and
 * {@link #stringValue()}.
 * <p>
 * Some uses of {@code Utf8Entry} represent field or method {@linkplain
 * TypeDescriptor#descriptorString() descriptor strings}, symbolically
 * represented as {@link ClassDesc} or {@link MethodTypeDesc}, depending on
 * where a {@code Utf8Entry} appear.  Entries representing such uses are created
 * with {@link ConstantPoolBuilder#utf8Entry(ClassDesc)} and {@link
 * ConstantPoolBuilder#utf8Entry(MethodTypeDesc)}, and they can be converted to
 * symbolic descriptors on a per-use-site basis, such as in {@link
 * AnnotationValue.OfClass#classSymbol()} and {@link MethodModel#methodTypeSymbol()}.
 * <p>
 * Unlike most constant pool entries, a UTF-8 entry is of flexible length: it is
 * represented as an array structure, with an {@code u2} for the data length in
 * bytes, followed by that number of bytes of Modified UTF-8 data.  It can
 * represent at most 65535 bytes of data due to the physical restrictions.
 *
 * @jvms 4.4.7 The {@code CONSTANT_Utf8_info} Structure
 * @see DataInput##modified-utf-8 Modified UTF-8
 * @since 24
 */
public sealed interface Utf8Entry
        extends CharSequence, AnnotationConstantValueEntry
        permits AbstractPoolEntry.Utf8EntryImpl {

    /**
     * {@return the string value for this entry}
     *
     * @apiNote
     * A {@code Utf8Entry} can be used directly as a {@link CharSequence} if
     * {@code String} functionalities are not strictly desired.  If only string
     * equivalence is desired, {@link #equalsString(String) equalsString} should
     * be used.  Reduction of string processing can significantly improve {@code
     * class} file reading performance.
     *
     * @see ConstantPoolBuilder#utf8Entry(String)
     */
    String stringValue();

    /**
     * {@return whether this entry describes the same string as the provided string}
     *
     * @param s the string to compare to
     */
    boolean equalsString(String s);

    /**
     * {@return whether this entry describes the descriptor string of this
     * field type}
     *
     * @param desc the field type
     * @since 25
     */
    boolean isFieldType(ClassDesc desc);

    /**
     * {@return whether this entry describes the descriptor string of this
     * method type}
     *
     * @param desc the method type
     * @since 25
     */
    boolean isMethodType(MethodTypeDesc desc);
}