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   * Copyright (c) 2012, 2013, 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
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   */
  
  package java.lang;
  
  import java.lang.annotation.*;
  
  /**
   * An informative annotation type used to indicate that an interface
   * type declaration is intended to be a <i>functional interface</i> as
   * defined by the Java Language Specification.
   *
   * Conceptually, a functional interface has exactly one abstract
   * method.  Since {@linkplain java.lang.reflect.Method#isDefault()
   * default methods} have an implementation, they are not abstract.  If
   * an interface declares an abstract method overriding one of the
   * public methods of {@code java.lang.Object}, that also does
   * <em>not</em> count toward the interface's abstract method count
   * since any implementation of the interface will have an
   * implementation from {@code java.lang.Object} or elsewhere.
   *
   * <p>Note that instances of functional interfaces can be created with
   * lambda expressions, method references, or constructor references.
   *
   * <p>If a type is annotated with this annotation type, compilers are
   * required to generate an error message unless:
   *
   * <ul>
   * <li> The type is an interface type and not an annotation type, enum, or class.
   * <li> The annotated type satisfies the requirements of a functional interface.
   * </ul>
   *
   * <p>However, the compiler will treat any interface meeting the
   * definition of a functional interface as a functional interface
   * regardless of whether or not a {@code FunctionalInterface}
   * annotation is present on the interface declaration.
   *
   * @jls 4.3.2. The Class Object
   * @jls 9.8 Functional Interfaces
   * @jls 9.4.3 Interface Method Body
   * @since 1.8
   */
  @Documented
  @Retention(RetentionPolicy.RUNTIME)
  @Target(ElementType.TYPE)
  public @interface FunctionalInterface {}
  