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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". When an API method is said to | |
| * accept or return a functional interface in this manner, such as "applies the | |
| * provided function to...", this is understood to mean a <i>non-null</i> | |
| * reference to an object implementing the appropriate functional interface, | |
| * unless potential nullity is explicitly specified. | |
| * | |
| * <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} (nullary 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 | |
| * @since 1.8 | |
| */ | |
| package java.util.function; |