package-info.java revision d052fb54474c6e3d99da861b02e4b49ac98790cc 
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25
26/**
27 * <em>Functional interfaces</em> provide target types for lambda expressions
28 * and method references.  Each functional interface has a single abstract
29 * method, called the <em>functional method</em> for that functional interface,
30 * to which the lambda expression's parameter and return types are matched or
31 * adapted.  Functional interfaces can provide a target type in multiple
32 * contexts, such as assignment context, method invocation, or cast context:
33 *
34 * <pre>{@code
35 *     // Assignment context
36 *     Predicate<String> p = String::isEmpty;
37 *
38 *     // Method invocation context
39 *     stream.filter(e -> e.getSize() > 10)...
40 *
41 *     // Cast context
42 *     stream.map((ToIntFunction) e -> e.getSize())...
43 * }</pre>
44 *
45 * <p>The interfaces in this package are general purpose functional interfaces
46 * used by the JDK, and are available to be used by user code as well.  While
47 * they do not identify a complete set of function shapes to which lambda
48 * expressions might be adapted, they provide enough to cover common
49 * requirements. Other functional interfaces provided for specific purposes,
50 * such as {@link java.io.FileFilter}, are defined in the packages where they
51 * are used.
52 *
53 * <p>The interfaces in this package are annotated with
54 * {@link java.lang.FunctionalInterface}. This annotation is not a requirement
55 * for the compiler to recognize an interface as a functional interface, but
56 * merely an aid to capture design intent and enlist the help of the compiler in
57 * identifying accidental violations of design intent.
58 *
59 * <p>Functional interfaces often represent abstract concepts like functions,
60 * actions, or predicates.  In documenting functional interfaces, or referring
61 * to variables typed as functional interfaces, it is common to refer directly
62 * to those abstract concepts, for example using "this function" instead of
63 * "the function represented by this object".  When an API method is said to
64 * accept or return a functional interface in this manner, such as "applies the
65 * provided function to...", this is understood to mean a <i>non-null</i>
66 * reference to an object implementing the appropriate functional interface,
67 * unless potential nullity is explicitly specified.
68 *
69 * <p>The functional interfaces in this package follow an extensible naming
70 * convention, as follows:
71 *
72 * <ul>
73 *     <li>There are several basic function shapes, including
74 *     {@link java.util.function.Function} (unary function from {@code T} to {@code R}),
75 *     {@link java.util.function.Consumer} (unary function from {@code T} to {@code void}),
76 *     {@link java.util.function.Predicate} (unary function from {@code T} to {@code boolean}),
77 *     and {@link java.util.function.Supplier} (nilary function to {@code R}).
78 *     </li>
79 *
80 *     <li>Function shapes have a natural arity based on how they are most
81 *     commonly used.  The basic shapes can be modified by an arity prefix to
82 *     indicate a different arity, such as
83 *     {@link java.util.function.BiFunction} (binary function from {@code T} and
84 *     {@code U} to {@code R}).
85 *     </li>
86 *
87 *     <li>There are additional derived function shapes which extend the basic
88 *     function shapes, including {@link java.util.function.UnaryOperator}
89 *     (extends {@code Function}) and {@link java.util.function.BinaryOperator}
90 *     (extends {@code BiFunction}).
91 *     </li>
92 *
93 *     <li>Type parameters of functional interfaces can be specialized to
94 *     primitives with additional type prefixes.  To specialize the return type
95 *     for a type that has both generic return type and generic arguments, we
96 *     prefix {@code ToXxx}, as in {@link java.util.function.ToIntFunction}.
97 *     Otherwise, type arguments are specialized left-to-right, as in
98 *     {@link java.util.function.DoubleConsumer}
99 *     or {@link java.util.function.ObjIntConsumer}.
100 *     (The type prefix {@code Obj} is used to indicate that we don't want to
101 *     specialize this parameter, but want to move on to the next parameter,
102 *     as in {@link java.util.function.ObjIntConsumer}.)
103 *     These schemes can be combined, as in {@code IntToDoubleFunction}.
104 *     </li>
105 *
106 *     <li>If there are specialization prefixes for all arguments, the arity
107 *     prefix may be left out (as in {@link java.util.function.ObjIntConsumer}).
108 *     </li>
109 * </ul>
110 *
111 * @see java.lang.FunctionalInterface
112 * @since 1.8
113 * @hide 1.8
114 */
115package java.util.function;
116