2020了你还不会java8新特性？（八）流源构造代码分析与总结

记录下来，然后给别人再讲，你就掌握了。

学完之后忘记了怎么办？记录下来。笔记博客。死记硬背是没有任何用的。

ReferencePipeline

/**
 * Abstract base class for an intermediate pipeline stage or pipeline source
 * stage implementing whose elements are of type {@code U}.
 */
//引用管道   
//ReferencePipeline  表示流的源阶段与中间阶段。
//ReferencePipeline.head表示流中的源阶段。
 abstract class ReferencePipeline<P_IN, P_OUT>
        extends AbstractPipeline<P_IN, P_OUT, Stream<P_OUT>>
        implements Stream<P_OUT>  {  
 }

AbstractPipeline

/**
 * Abstract base class for "pipeline" classes, which are the core
 * implementations of the Stream interface and its primitive specializations.
 * Manages construction and evaluation of stream pipelines.
 *  
 * <p>An {@code AbstractPipeline} represents an initial portion of a stream
 * pipeline, encapsulating a stream source and zero or more intermediate
 * operations.  The individual {@code AbstractPipeline} objects are often
 * referred to as <em>stages</em>, where each stage describes either the stream
 * source or an intermediate operation.
 流管道的初始的一部分。
 *
 * <p>A concrete intermediate stage is generally built from an
 * {@code AbstractPipeline}, a shape-specific pipeline class which extends it
 * (e.g., {@code IntPipeline}) which is also abstract, and an operation-specific
 * concrete class which extends that.  {@code AbstractPipeline} contains most of
 * the mechanics of evaluating the pipeline, and implements methods that will be
 * used by the operation; the shape-specific classes add helper methods for
 * dealing with collection of results into the appropriate shape-specific
 * containers.
 *避免自动拆箱和装箱操作。
 * <p>After chaining a new intermediate operation, or executing a terminal
 * operation, the stream is considered to be consumed, and no more intermediate
 * or terminal operations are permitted on this stream instance.
 * 当链接完一个新的中间操作或者执行了终止操作之后， 这个流被认为被消费了。不允许再被操作了。
 * @implNote
 * <p>For sequential streams, and parallel streams without
 * <a href="package-summary.html#StreamOps">stateful intermediate
 * operations</a>, parallel streams, pipeline evaluation is done in a single
 * pass that "jams" all the operations together.  For parallel streams with
 * stateful operations, execution is divided into segments, where each
 * stateful operations marks the end of a segment, and each segment is
 * evaluated separately and the result used as the input to the next
 * segment.  In all cases, the source data is not consumed until a terminal
 * operation begins.
  只有终止操作开始的时候，源数据才会被消费。
 * @param <E_IN>  type of input elements
 * @param <E_OUT> type of output elements
 * @param <S> type of the subclass implementing {@code BaseStream}
 * @since 1.8
 */
abstract class AbstractPipeline<E_IN, E_OUT, S extends BaseStream<E_OUT, S>>
        extends PipelineHelper<E_OUT> implements BaseStream<E_OUT, S> {
}

内部类，和lambda表达式之间的关系。

本质上内部类和lambda不是一回事。只是能完成相同的操作。

lambda不是匿名内部类的语法糖，或者说是缩写。是一种新的形式。

public class LambdaTest {
    //内部类，和lambda表达式之间的关系。
    Runnable r1 = () -> System.out.println(this); // this表示当前类的对象

    //匿名内部类
    Runnable r2 = new Runnable() {  //
        @Override
        public void run() {
            System.out.println(this);
            // this 表示匿名内部类的对象
        }
    };


    public static void main(String[] args) {
        LambdaTest lambdaTest = new LambdaTest();

        Thread t1 = new Thread(lambdaTest.r1);
        t1.start();

        System.out.println("- - -- - ");

        Thread t2 = new Thread(lambdaTest.r2);
        t2.start();
        //输出结果。
        //com.sinosoft.lis.test.LambdaTest@62661526
        //com.sinosoft.lis.test.LambdaTest$1@59a30351
    }

}

使用了模板方法模式。

流是惰性的，是延迟操作的。遇到终止操作时，才会执行操作。

TerminalOp。终止操作的接口类。

终止操作只有四种类型， findOp foreachOp matchOp reduceOp

PipelineHelper

stream中间操作与终止操作层次体系分析与设计思想分析

中间操作

BaseStream -》 AbStractpipeline -》ReferencePipeline -》 Head || StatelessOP || statefulOp

最顶层的源很多源的成员变量管道构造流源无状态的中间操作有状态的中间操作

流是惰性的，是延迟操作的。遇到终止操作时，才会执行操作。再没有终止操作之前，在整合中间操作（Sink）。

终止操作

TerminalOp -》 FindOp || ForeachOp || MatchOp || reduceOp

最顶层的

TerminalSink

终止的饮水槽。