1 /*
   2  * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.lang.invoke;
  26 
  27 import java.lang.annotation.TrackableConstant;
  28 
  29 /**
  30  * Descriptor for an entry in the classfile constant pool.
  31  *
  32  * A {@linkplain Constable} should be defined entirely in terms of other
  33  * {@linkplain Constable} types.  The types {@link Integer}, {@link Long},
  34  * {@link Float}, {@link Double}, and {@link String} implement
  35  * {@linkplain Constable}.  Implementation classes should be value-based.
  36  *
  37  * Like names in the constant pool, names in a constant descriptor are independent
  38  * of a class loader.  When a {@linkplain Constable} is intrinsified, it is
  39  * interpreted relative to the class loader that loaded the class in which the
  40  * intrinsic appears (just like names that appear in that classes constant pool.)
  41  * When resolved through the method {@link #resolveConstant}, an explicit
  42  * {@link MethodHandles.Lookup} must be provided.
  43  *
  44  * The intrinsifiable methods in {@link Intrinsics} take {@linkplain Constable}
  45  * arguments.
  46  *
  47  * @param <T> The type to which this constant pool entry resolves
  48  *
  49  * @see Constables
  50  * @see Intrinsics
  51  * @see TrackableConstant
  52  */
  53 public interface Constable<T> {
  54     /**
  55      * Resolve this constant, relative to the provided lookup.
  56      * @param lookup the lookup to use to resolve this constant
  57      * @return the constant
  58      * @throws ReflectiveOperationException if the constant refers to a class
  59      * or member that does not exist, or is not accessible to the class described
  60      * by {@code lookup}
  61      */
  62     T resolveConstant(MethodHandles.Lookup lookup) throws ReflectiveOperationException;
  63 }