77 lines
3.7 KiB
Java
77 lines
3.7 KiB
Java
/*
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* Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.lang.constant;
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import java.lang.invoke.MethodHandle;
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import java.lang.invoke.MethodType;
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import java.lang.invoke.VarHandle;
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import java.util.Optional;
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/**
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* Represents a type which is <em>constable</em>. A constable type is one whose
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* values are constants that can be represented in the constant pool of a Java
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* classfile as described in JVMS 4.4, and whose instances can describe themselves
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* nominally as a {@link ConstantDesc}.
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*
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* <p>Some constable types have a native representation in the constant pool:
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* {@link String}, {@link Integer}, {@link Long}, {@link Float},
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* {@link Double}, {@link Class}, {@link MethodType}, and {@link MethodHandle}.
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* The types {@link String}, {@link Integer}, {@link Long}, {@link Float},
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* and {@link Double} serve as their own nominal descriptors; {@link Class},
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* {@link MethodType}, and {@link MethodHandle} have corresponding nominal
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* descriptors {@link ClassDesc}, {@link MethodTypeDesc}, and {@link MethodHandleDesc}.
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*
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* <p>Other reference types can be constable if their instances can describe
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* themselves in nominal form as a {@link ConstantDesc}. Examples in the Java SE
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* Platform API are types that support Java language features such as {@link Enum},
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* and runtime support classes such as {@link VarHandle}. These are typically
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* described with a {@link DynamicConstantDesc}, which describes dynamically
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* generated constants (JVMS 4.4.10).
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*
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* <p>The nominal form of an instance of a constable type is obtained via
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* {@link #describeConstable()}. A {@linkplain Constable} need
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* not be able to (or may choose not to) describe all its instances in the form of
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* a {@link ConstantDesc}; this method returns an {@link Optional} that can be
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* empty to indicate that a nominal descriptor could not be created for an instance.
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* (For example, {@link MethodHandle} will produce nominal descriptors for direct
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* method handles, but not necessarily those produced by method handle
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* combinators.)
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* @jvms 4.4 The Constant Pool
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* @jvms 4.4.10 The {@code CONSTANT_Dynamic_info} and {@code CONSTANT_InvokeDynamic_info} Structures
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*
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* @since 12
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*/
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public interface Constable {
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/**
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* Returns an {@link Optional} containing the nominal descriptor for this
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* instance, if one can be constructed, or an empty {@link Optional}
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* if one cannot be constructed.
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*
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* @return An {@link Optional} containing the resulting nominal descriptor,
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* or an empty {@link Optional} if one cannot be constructed.
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*/
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Optional<? extends ConstantDesc> describeConstable();
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}
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