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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

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 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

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 *

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package java.util.stream;

import java.util.Spliterator;

/**

 * An operation in a stream pipeline that takes a stream as input and produces

 * a result or side-effect.  A {@code TerminalOp} has an input type and stream

 * shape, and a result type.  A {@code TerminalOp} also has a set of

 * <em>operation flags</em> that describes how the operation processes elements

 * of the stream (such as short-circuiting or respecting encounter order; see

 * {@link StreamOpFlag}).

 *

 * <p>A {@code TerminalOp} must provide a sequential and parallel implementation

 * of the operation relative to a given stream source and set of intermediate

 * operations.

 *

 * @param <E_IN> the type of input elements

 * @param <R>    the type of the result

 * @since 1.8

 */

interface TerminalOp<E_IN, R> {

    /**

     * Gets the shape of the input type of this operation.

     *

     * @implSpec The default returns {@code StreamShape.REFERENCE}.

     *

     * @return StreamShape of the input type of this operation

     */

    default StreamShape inputShape() { return StreamShape.REFERENCE; }

    /**

     * Gets the stream flags of the operation.  Terminal operations may set a

     * limited subset of the stream flags defined in {@link StreamOpFlag}, and

     * these flags are combined with the previously combined stream and

     * intermediate operation flags for the pipeline.

     *

     * @implSpec The default implementation returns zero.

     *

     * @return the stream flags for this operation

     * @see StreamOpFlag

     */

    default int getOpFlags() { return 0; }

    /**

     * Performs a parallel evaluation of the operation using the specified

     * {@code PipelineHelper}, which describes the upstream intermediate

     * operations.

     *

     * @implSpec The default performs a sequential evaluation of the operation

     * using the specified {@code PipelineHelper}.

     *

     * @param helper the pipeline helper

     * @param spliterator the source spliterator

     * @return the result of the evaluation

     */

    default <P_IN> R evaluateParallel(PipelineHelper<E_IN> helper,

                                      Spliterator<P_IN> spliterator) {

        if (Tripwire.ENABLED)

            Tripwire.trip(getClass(), "{0} triggering TerminalOp.evaluateParallel serial default");

        return evaluateSequential(helper, spliterator);

    }

    /**

     * Performs a sequential evaluation of the operation using the specified

     * {@code PipelineHelper}, which describes the upstream intermediate

     * operations.

     *

     * @param helper the pipeline helper

     * @param spliterator the source spliterator

     * @return the result of the evaluation

     */

    <P_IN> R evaluateSequential(PipelineHelper<E_IN> helper,

                                Spliterator<P_IN> spliterator);

}