BaseStream.java

/*
 * 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
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package java.util.stream;

import java.util.Iterator;
import java.util.Spliterator;

/**
 * Base interface for streams, which are sequences of elements supporting sequential and parallel aggregate operations.
 * The following example illustrates an aggregate operation using the stream types {@link Stream} and {@link IntStream}, computing the sum of the weights of the red widgets:
 *
 * <pre>{@code
 *     int sum = widgets.stream()
 *                      .filter(w -> w.getColor() == RED)
 *                      .mapToInt(w -> w.getWeight())
 *                      .sum();
 * }</pre>
 *
 * See the class documentation for {@link Stream} and the package documentation for <a href="package-summary.html">java.util.stream</a> for additional specification of streams,
 * stream operations, stream pipelines, and parallelism, which governs the behavior of all stream types.
 *
 * @param <T> the type of the stream elements
 * @param <S> the type of the stream implementing {@code BaseStream}
 *
 * @see Stream
 * @see IntStream
 * @see LongStream
 * @see DoubleStream
 * @see <a href="package-summary.html">java.util.stream</a>
 * @since 1.8
 */
// 流的基本接口；流是支持顺序操作和并行操作的元素序列
public interface BaseStream<T, S extends BaseStream<T, S>> extends AutoCloseable {
    
    /**
     * Returns a spliterator for the elements of this stream.
     *
     * <p>This is a <a href="package-summary.html#StreamOps">terminal
     * operation</a>.
     *
     * <p>
     * The returned spliterator should report the set of characteristics derived
     * from the stream pipeline (namely the characteristics derived from the
     * stream source spliterator and the intermediate operations).
     * Implementations may report a sub-set of those characteristics.  For
     * example, it may be too expensive to compute the entire set for some or
     * all possible stream pipelines.
     *
     * @return the element spliterator for this stream
     */
    // 返回当前阶段的流的流迭代器；如果遇到并行流的有状态的中间阶段，则需要特殊处理
    Spliterator<T> spliterator();
    
    /**
     * Returns an iterator for the elements of this stream.
     *
     * <p>This is a <a href="package-summary.html#StreamOps">terminal operation</a>.
     *
     * @return the element iterator for this stream
     */
    // 将当前阶段的流的Spliterator适配为Iterator
    Iterator<T> iterator();
    
    /**
     * Returns whether this stream, if a terminal operation were to be executed,
     * would execute in parallel.  Calling this method after invoking an
     * terminal stream operation method may yield unpredictable results.
     *
     * @return {@code true} if this stream would execute in parallel if executed
     */
    // 判断当前流是否需要并行执行(是否为并行流)
    boolean isParallel();
    
    /**
     * Returns an equivalent stream that is
     * <a href="package-summary.html#Ordering">unordered</a>.  May return
     * itself, either because the stream was already unordered, or because
     * the underlying stream state was modified to be unordered.
     *
     * <p>This is an <a href="package-summary.html#StreamOps">intermediate
     * operation</a>.
     *
     * @return an unordered stream
     */
    // 中间操作：将当前流设置为无序流后返回
    S unordered();
    
    /**
     * Returns an equivalent stream that is sequential.  May return
     * itself, either because the stream was already sequential, or because
     * the underlying stream state was modified to be sequential.
     *
     * <p>This is an <a href="package-summary.html#StreamOps">intermediate
     * operation</a>.
     *
     * @return a sequential stream
     */
    // 中间操作：将当前流设置为顺序流后返回
    S sequential();
    
    /**
     * Returns an equivalent stream that is parallel.  May return
     * itself, either because the stream was already parallel, or because
     * the underlying stream state was modified to be parallel.
     *
     * <p>This is an <a href="package-summary.html#StreamOps">intermediate
     * operation</a>.
     *
     * @return a parallel stream
     */
    // 中间操作：将当前流设置为并行流后返回
    S parallel();
    
    /**
     * Returns an equivalent stream with an additional close handler.  Close
     * handlers are run when the {@link #close()} method
     * is called on the stream, and are executed in the order they were
     * added.  All close handlers are run, even if earlier close handlers throw
     * exceptions.  If any close handler throws an exception, the first
     * exception thrown will be relayed to the caller of {@code close()}, with
     * any remaining exceptions added to that exception as suppressed exceptions
     * (unless one of the remaining exceptions is the same exception as the
     * first exception, since an exception cannot suppress itself.)  May
     * return itself.
     *
     * <p>This is an <a href="package-summary.html#StreamOps">intermediate
     * operation</a>.
     *
     * @param closeHandler A task to execute when the stream is closed
     *
     * @return a stream with a handler that is run if the stream is closed
     */
    // 中间操作：为当前流设置一个关闭回调，并返回当前流自身
    S onClose(Runnable closeHandler);
    
    /**
     * Closes this stream, causing all close handlers for this stream pipeline to be called.
     *
     * @see AutoCloseable#close()
     */
    // 关闭此当前阶段的流，并执行关闭回调
    @Override
    void close();
    
}