| /* | |
| * Copyright (c) 2022, 2024, 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; | |
| import java.lang.classfile.attribute.CodeAttribute; | |
| import java.lang.classfile.instruction.LabelTarget; | |
| import java.util.ListIterator; | |
| import jdk.internal.classfile.impl.LabelImpl; | |
| /** | |
| * A marker for a position within the instructions of a method body. The | |
| * position is a cursor position in the list of instructions, similar to that | |
| * of a {@link ListIterator}. | |
| * | |
| * <h2 id="reading">Reading Labels</h2> | |
| * Labels read from {@code class} files represent positions in the {@code code} | |
| * array of a {@link CodeAttribute Code} attribute. It is associated with a | |
| * <dfn>{@index bci}</dfn> (bytecode index), also known as <dfn>{@index pc}</dfn> | |
| * (program counter), the index into the {@code code} array; the actual cursor | |
| * position is immediately before the given index, so a label at the beginning | |
| * of the instructions has bci {@code 0}, and a label at the end of the | |
| * instructions has bci {@link CodeAttribute#codeLength codeLength() + 1}. The | |
| * bci can be inspected through {@link CodeAttribute#labelToBci | |
| * CodeAttribute::labelToBci}. | |
| * <p> | |
| * In generic {@link CodeModel}s, a label may not have a bci value; the position | |
| * of a label can be found by searching for the corresponding {@link LabelTarget} | |
| * within that model. | |
| * | |
| * <h2 id="writing">Writing Labels</h2> | |
| * Many models in {@link java.lang.classfile} refer to labels. To write a | |
| * label, a label must be obtained, it must be bound to a {@link CodeBuilder}. | |
| * <p> | |
| * To obtain a label: | |
| * <ul> | |
| * <li>Use a label read from other models. | |
| * <li>Use pre-defined labels from a {@link CodeBuilder}, such as {@link | |
| * CodeBuilder#startLabel() CodeBuilder::startLabel}, {@link CodeBuilder#endLabel | |
| * CodeBuilder::endLabel}, or {@link CodeBuilder.BlockCodeBuilder#breakLabel | |
| * BlockCodeBuilder::breakLabel}. They are already bound. | |
| * <li>Create labels with {@link CodeBuilder#newLabel CodeBuilder::newLabel} or | |
| * {@link CodeBuilder#newBoundLabel CodeBuilder::newBoundLabel}. | |
| * </ul> | |
| * <p> | |
| * A label must be bound exactly once in the {@code CodeBuilder} where it is | |
| * used; otherwise, writing fails. To bind an unbound label: | |
| * <ul> | |
| * <li>Send a read {@link LabelTarget} to a {@code CodeBuilder}. | |
| * <li>Use {@link CodeBuilder#labelBinding CodeBuilder::labelBinding}. | |
| * </ul> | |
| * Note that a label read from another model is not automatically bound in a | |
| * {@code CodeBuilder}; they are separate entities and the label is bound to | |
| * different positions in them. | |
| * | |
| * @see CodeAttribute#labelToBci CodeAttribute::labelToBci | |
| * @see CodeBuilder#newLabel CodeBuilder::newLabel | |
| * @see CodeBuilder#labelBinding CodeBuilder::labelBinding | |
| * @since 24 | |
| */ | |
| public sealed interface Label | |
| permits LabelImpl { | |
| } |