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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, called the <em>functional method</em> for that functional interface,

 * 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>{@code

 *     // Assignment context

 *     Predicate<String> p = String::isEmpty;

 *

 *     // Method invocation context

 *     stream.filter(e -> e.getSize() > 10)...

 *

 *     // Cast context

 *     stream.map((ToIntFunction) e -> e.getSize())...

 * }</pre>

 *

 * <p>The interfaces in this package are general purpose 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. Other functional interfaces provided for specific purposes,

 * such as {@link java.io.FileFilter}, are defined in the packages where they

 * are used.

 *

 * <p>The interfaces in this package are annotated with

 * {@link java.lang.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>Functional interfaces often represent abstract concepts like functions,

 * actions, or predicates.  In documenting functional interfaces, or referring

 * to variables typed as functional interfaces, it is common to refer directly

 * to those abstract concepts, for example using "this function" instead of

 * "the function represented by this object".

 *

 * <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} (unary function from {@code T} to {@code R}),

 *     {@link java.util.function.Consumer} (unary function from {@code T} to {@code void}),

 *     {@link java.util.function.Predicate} (unary function from {@code T} to {@code boolean}),

 *     and {@link java.util.function.Supplier} (nilary function to {@code R}).

 *     </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} (binary function from {@code T} and

 *     {@code U} to {@code 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,

 *     as in {@link java.util.function.ObjIntConsumer}.)

 *     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;