Java8 教程第八章之Array to Stream

本套JAVA8教程由于是有英文翻译过来的,如果有翻译不对的地方还请多多包涵。

本节课先简单的介绍下Java8有哪些新特性,对于Java6/7版本做出哪些更改.那废话不多说,赶紧开始今天的课程吧.

在Java 8里，你可以用Arrays.stream 或 Stream.of来将数组转换成流。

对象数组

• 对于对象数组，Arrays.stream 和 Stream.of方法都可以返回同样的输出结果。
  例子:

public static void main(String[] args) {
        String[] array = {"a", "b", "c", "d", "e"};
        //Arrays.stream 调用
        Stream stream1 = Arrays.stream(array);
        stream1.forEach(System.out::println);

        //Stream.of调用
        Stream stream2 = Stream.of(array);
        stream2.forEach(System.out::println);
    }

请注意 对于对象数组，Stream.of方法会在内部调用Arrays.stream

原始数组

看下代码

public static void main(String[] args) {
        int[] intArray = {1, 2, 3, 4, 5};
        // 1. Arrays.stream -> IntStream
        IntStream intStream1 = Arrays.stream(intArray);
        intStream1.forEach(System.out::println);
        // 2. Stream.of ->; Stream
        Stream temp = Stream.of(intArray);
        // Cant print Stream directly, convert / flat it to IntStream
        IntStream intStream2 = temp.flatMapToInt(Arrays::stream);
        intStream2.forEach(System.out::println);
    }

其实这样看并么有看到本质上的不同,那这次咱们看下源码实现吧

1. 对象数组
   Arrays.java

  /**
     * Returns a sequential {@link Stream} with the specified array as its
     * source.
     *
     * @param  The type of the array elements
     * @param array The array, assumed to be unmodified during use
     * @return a {@code Stream} for the array
     * @since 1.8
     */
    public static  Stream stream(T[] array) {
        return stream(array, 0, array.length);
    }

Stream.java

/**
     * Returns a sequential ordered stream whose elements are the specified values.
     *
     * @param  the type of stream elements
     * @param values the elements of the new stream
     * @return the new stream
     */
    @SafeVarargs
    @SuppressWarnings("varargs") // Creating a stream from an array is safe
    public static Stream of(T... values) {
        return Arrays.stream(values);
    }

从这我们不难看出对于对象数组，Stream.of方法会在内部调用Arrays.stream。
那下面咱们再看下原始数组的调用
Arrays.java

  /**
     * Returns a sequential {@link IntStream} with the specified array as its
     * source.
     *
     * @param array the array, assumed to be unmodified during use
     * @return an {@code IntStream} for the array
     * @since 1.8
     */
    public static IntStream stream(int[] array) {
        return stream(array, 0, array.length);
    }

Stream.java

/**
     * Returns a sequential {@code Stream} containing a single element.
     *
     * @param t the single element
     * @param  the type of stream elements
     * @return a singleton sequential stream
     */
    public static Stream of(T t) {
        return StreamSupport.stream(new Streams.StreamBuilderImpl<>(t), false);
    }

该用哪一个呢?
对于对象数组，都会调用Arrays.stream(参见示例1，JDK源代码)。 对于原始数组，更推荐Arrays.stream，因为它直接返回固定大小的IntStream，更易于操作。

有不同意见的小伙伴们积极留言哦. 一起讨论!