1/*
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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5 * This code is free software; you can redistribute it and/or modify it
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7 * published by the Free Software Foundation.  Oracle designates this
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10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
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24 */
25package java.util.stream;
26
27import java.util.Spliterator;
28
29/**
30 * An operation in a stream pipeline that takes a stream as input and produces
31 * a result or side-effect.  A {@code TerminalOp} has an input type and stream
32 * shape, and a result type.  A {@code TerminalOp} also has a set of
33 * <em>operation flags</em> that describes how the operation processes elements
34 * of the stream (such as short-circuiting or respecting encounter order; see
35 * {@link StreamOpFlag}).
36 *
37 * <p>A {@code TerminalOp} must provide a sequential and parallel implementation
38 * of the operation relative to a given stream source and set of intermediate
39 * operations.
40 *
41 * @param  the type of input elements
42 * @param <R>    the type of the result
43 * @since 1.8
44 */
45interface TerminalOp<E_IN, R> {
46    /**
47     * Gets the shape of the input type of this operation.
48     *
49     * @implSpec The default returns {@code StreamShape.REFERENCE}.
50     *
51     * @return StreamShape of the input type of this operation
52     */
53    default StreamShape inputShape() { return StreamShape.REFERENCE; }
54
55    /**
56     * Gets the stream flags of the operation.  Terminal operations may set a
57     * limited subset of the stream flags defined in {@link StreamOpFlag}, and
58     * these flags are combined with the previously combined stream and
59     * intermediate operation flags for the pipeline.
60     *
61     * @implSpec The default implementation returns zero.
62     *
63     * @return the stream flags for this operation
64     * @see StreamOpFlag
65     */
66    default int getOpFlags() { return 0; }
67
68    /**
69     * Performs a parallel evaluation of the operation using the specified
70     * {@code PipelineHelper}, which describes the upstream intermediate
71     * operations.
72     *
73     * @implSpec The default performs a sequential evaluation of the operation
74     * using the specified {@code PipelineHelper}.
75     *
76     * @param helper the pipeline helper
77     * @param spliterator the source spliterator
78     * @return the result of the evaluation
79     */
80    default <P_IN> R evaluateParallel(PipelineHelper<E_IN> helper,
81                                      Spliterator<P_IN> spliterator) {
82        if (Tripwire.ENABLED)
83            Tripwire.trip(getClass(), "{0} triggering TerminalOp.evaluateParallel serial default");
84        return evaluateSequential(helper, spliterator);
85    }
86
87    /**
88     * Performs a sequential evaluation of the operation using the specified
89     * {@code PipelineHelper}, which describes the upstream intermediate
90     * operations.
91     *
92     * @param helper the pipeline helper
93     * @param spliterator the source spliterator
94     * @return the result of the evaluation
95     */
96    <P_IN> R evaluateSequential(PipelineHelper<E_IN> helper,
97                                Spliterator<P_IN> spliterator);
98}
99