| /* |
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| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
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| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that 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, 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} (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 |
| * @since 1.8 |
| */ |
| package java.util.function; |