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
  29  * a result or side-effect.  A {@code TerminalOp} has an input type and stream
  30  * shape, and a result type.  A {@code TerminalOp} also has a set of
  31  * <em>operation flags</em> that describes how the operation processes elements
  32  * of the stream (such as short-circuiting or respecting encounter order; see
  33  * {@link StreamOpFlag}).
  34  *
  35  * <p>A {@code TerminalOp} must provide a sequential and parallel implementation
  36  * of the operation relative to a given stream source and set of intermediate
  37  * operations.
  38  *
  39  * @param <E_IN> The type of input elements
  40  * @param <R>    The type of the result
  41  * @see StatefulOp
  42  * @see IntermediateOp
  43  * @since 1.8
  44  */
  45 interface 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      * @return Shape of the input type of this operation
  51      */
  52     default StreamShape inputShape() { return StreamShape.REFERENCE; }
  53 
  54     /**
  55      * Gets the properties of the operation.  Terminal operations may set a
  56      * limited subset of the stream flags defined in {@link StreamOpFlag}, and
  57      * these flags are combined with the previously combined stream and
  58      * intermediate operation flags for the pipeline.
  59      *
  60      * @implSpec The default implementation returns zero
  61      * @return the properties of the operation
  62      * @see {@link StreamOpFlag}
  63      */
  64     default int getOpFlags() { return 0; }
  65 
  66     /**
  67      * Performs a parallel evaluation of the operation using the specified
  68      * {@code PipelineHelper}, which describes the stream source and upstream
  69      * intermediate operations.
  70      *
  71      * @implSpec The default performs a sequential evaluation of the operation
  72      * using the specified {@code PipelineHelper}
  73      *
  74      * @param helper the pipeline helper
  75      * @param <P_IN> the type of elements in the pipeline source
  76      * @return the result of the evaluation
  77      */
  78     default <P_IN> R evaluateParallel(PipelineHelper<P_IN, E_IN> helper) {
  79         if (Tripwire.ENABLED)
  80             Tripwire.trip(getClass(), "{0} triggering TerminalOp.evaluateParallel serial default");
  81         return evaluateSequential(helper);
  82     }
  83 
  84     /**
  85      * Performs a sequential evaluation of the operation using the specified
  86      * {@code PipelineHelper}, which describes the stream source and upstream
  87      * intermediate operations.
  88      *
  89      * @param helper the pipeline helper
  90      * @param <P_IN> the type of elements in the pipeline source
  91      * @return the result of the evaluation
  92      */
  93     <P_IN> R evaluateSequential(PipelineHelper<P_IN, E_IN> helper);
  94 }