Java example source code file (TerminalOp.java)

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Java - Java tags/keywords

p_in, spliterator, streamshape, terminalop, util

The TerminalOp.java Java example source code

/*
 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * 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,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
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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 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 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 helper,
                                Spliterator<P_IN> spliterator);
}