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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
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 * accompanied this code).
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/**
 * <em>Functional interfaces</em> provide target types for lambda expressions
 * and method references.  Each functional interface has a single abstract method
 * to which the lambda expression's parameter and return types are matched or
 * adapted.  Functional interfaces can provide a target type in multiple contexts,
 * such as assignment context, method invocation, or cast context:
 *
 * <pre>
 *     Predicate&lt;String> p = String::isEmpty;
 *
 *     stream.filter(e -> e.getSize() > 10)...
 *
 *     stream.map((ToIntFunction) e -> e.getSize())...
 * </pre>
 *
 * <p>The interfaces in this package are functional interfaces used by the JDK,
 * and are available to be used by user code as well.  While they do not identify
 * a complete set of function shapes to which lambda expressions might be adapted,
 * they provide enough to cover common requirements.
 *
 * <p>The interfaces in this package are annotated with @{link FunctionalInterface}.
 * This annotation is not a requirement for the compiler to recognize an interface
 * as a functional interface, but merely an aid to capture design intent and enlist the
 * help of the compiler in identifying accidental violations of design intent.
 *
 * <p>The functional interfaces in this package follow an extensible naming convention,
 * as follows:
 *
 * <ul>
 *     <li>There are several basic function shapes, including {@link java.util.function.Function} ({@code T -> R}),
 *     {@link java.util.function.Consumer} ({@code T -> void}),
 *     {@link java.util.function.Predicate} ({@code T -> boolean}),
 *     and {@link java.util.function.Supplier} ({@code () -> T}).
 *     </li>
 *     <li>Function shapes have a natural arity based on how they are most commonly used.
 *     The basic shapes can be modified by an arity prefix to indicate a different arity,
 *     such as {@link java.util.function.BiFunction} ({@code (T, U) -> R}).
 *     </li>
 *     <li>There are additional derived function shapes which extend the basic function
 *     shapes, including {@link java.util.function.UnaryOperator} (extends {@code Function}) and
 *     {@link java.util.function.BinaryOperator} (extends {@code BiFunction}).
 *     </li>
 *     <li>Type parameters of functional interfaces can be specialized to primitives with
 *     additional type prefixes.  To specialize the return type for a type that has both
 *     generic return type and generic arguments, we prefix {@code ToXxx}, as in
 *     {@link java.util.function.ToIntFunction}.  Otherwise, type arguments are specialized left-to-right,
 *     as in {@link java.util.function.DoubleConsumer} or {@link java.util.function.ObjIntConsumer}.
 *     (The type prefix {@code Obj} is used to indicate that we don't want to specialize this parameter,
 *     but want to move on to the next parameter.)  These schemes can be combined as in {@code IntToDoubleFunction}.
 *     </li>
 *     <li>If there are specialization prefixes for all arguments, the arity prefix may be left
 *     out (as in {@link java.util.function.ObjIntConsumer}).
 *     </li>
 * </ul>
 *
 * @see java.lang.FunctionalInterface
 */
package java.util.function;