1 /*
   2  * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  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  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.util.stream;
  26 
  27 /**
  28  * An operation in a stream pipeline that takes a stream as input and produces a result or side-effect.
  29  * A {@code TerminalOp} has an input type and stream shape, and a result type.  A {@code TerminalOp} also
  30  * has a set of <em>operation flags</em> that describes how the operation processes elements of the stream
  31  * (such as short-circuiting or respecting encounter order; see {@link StreamOpFlag}).
  32  *
  33  * <p>A {@code TerminalOperation} must provide a sequential and parallel implementation of the operation relative
  34  * to a given stream source and set of intermediate operations.
  35  *
  36  * @param <E_IN> The type of input elements
  37  * @param <R>    The type of the result
  38  * @see StatefulOp
  39  * @see IntermediateOp
  40  * @since 1.8
  41  */
  42 interface TerminalOp<E_IN, R> {
  43     /**
  44      * Get the shape of the input type of this operation
  45      * @implSpec The default returns {@code StreamShape.REFERENCE}
  46      * @return Shape of the input type of this operation
  47      */
  48     default StreamShape inputShape() { return StreamShape.REFERENCE; }
  49 
  50     /**
  51      * Get the properties of the operation.  Terminal operations may set a limited subset of the stream
  52      * flags defined in {@link StreamOpFlag}, and these flags are combined with the previously combined stream and
  53      * intermediate operation flags for the pipeline.
  54      * @implSpec The default implementation returns zero
  55      * @return the properties of the operation
  56      * @see {@link StreamOpFlag}
  57      */
  58     default int getOpFlags() { return 0; }
  59 
  60     /**
  61      * Perform a parallel evaluation of the operation using the specified {@code PipelineHelper}, which describes
  62      * the stream source and upstream intermediate operations.
  63      * @implSpec The default performs a sequential evaluation of the operation using the
  64      * specified {@code PipelineHelper}
  65      *
  66      * @param helper the pipeline helper
  67      * @param <P_IN> the type of elements in the pipeline source
  68      * @return the result of the evaluation
  69      */
  70     default <P_IN> R evaluateParallel(PipelineHelper<P_IN, E_IN> helper) {
  71         if (Tripwire.enabled)
  72             Tripwire.trip(getClass(), "{0} triggering TerminalOp.evaluateParallel serial default");
  73         return evaluateSequential(helper);
  74     }
  75 
  76     /**
  77      * Perform a sequential evaluation of the operation using the specified {@code PipelineHelper}, which describes
  78      * the stream source and upstream intermediate operations.
  79      *
  80      * @param helper the pipeline helper
  81      * @param <P_IN> the type of elements in the pipeline source
  82      * @return the result of the evaluation
  83      */
  84     <P_IN> R evaluateSequential(PipelineHelper<P_IN, E_IN> helper);
  85 }