Java8 new stateless intermediate operating characteristics Stream

Stateless intermediate operation

Java8 practice examples of new features Stream

Intermediate stateless operation, may be processed in a single individual data. For example: When an element filter (filtering), it may be determined, for example map (map) ...

Filtering filter
of map
flat clip of flatMap
pass Li peek

Filtration filter

Receiving a predicate assertion, boolean Pridicate <T> to determine whether a property that the filter according to the type of the return value.

// 过滤 filter
@Test
public void filterTest() {
    list.stream()
            //过滤掉所有小于2000的商品
            .filter(sku -> sku.getSkuPrice() > 2000)
            .forEach(item -> 
                    System.out.println(
                            JSON.toJSONString(
                                    item.getSkuName()+item.getSkuPrice(),
                                    true)));
    /**
     * 输出的结果
     * "无人机4999.0"
     * "VR一体机2299.0"
     * "跑步机2699.0"
     */

Map map

Stream map support method, receiving a Function <T, R> Interface function type, this method will be applied each element, and maps them into a new stream. In fact, in the above example it has been used very much, for example, receives a SKu type of flow, but after later map, the return of String streams.

//映射 map
@Test
public void mapTest() {
    list.stream()
            //用方法引用取出来sku中的所有的商品名称
            .map(Sku::getSkuName)
            .forEach(item -> System.out.println(item));
    /**
     * 无人机
     * VR一体机
     * 纯色衬衫
     * 牛仔裤
     * 跑步机
     * Java编程思想
     * Java核心技术
     * 算法
     * TensorFlow进阶指南
     */
}

Flat flatMap

flatMap method is to let each of the values ​​you have a stream flows into another, all the streams are connected into a side stream: Cases

//扁夹化 flatMap
@Test
public void flatMap() {
    List<String> words = Arrays.asList("Java 8", "Lambdas", "In", "Action");
    List<String[]> listStringArrays = words.stream()
            //分割每一个单词
            .map(word -> word.split(""))
            //对所有的元素去重
            .distinct()
            //收集成list集合
            .collect(Collectors.toList());

    listStringArrays.forEach(arr ->
            System.out.println(Arrays.toString(arr)));
    /**
     * 非扁平化
     * 这是把每一个数组当成了一整个元素，
     * 然后对一整个数组进行去重，
     * 如果数组没有重复的就不会去重
     * [J, a, v, a,  , 8]
     * [L, a, m, b, d, a, s]
     * [I, n]
     * [A, c, t, i, o, n]
     */
    List<String> listString = words.stream()
            //映射成String[]数组流
            .map(word -> word.split(""))
            //扁平化
            .flatMap(Arrays::stream)
            //去重
            .distinct()
            //排序
            .sorted()
            //收集
            .collect(Collectors.toList());
    listString.forEach(System.out::println);
    /**
     * 扁平化是把所有的数组map映射出来的数组流
     * 转换成一个流，而不是一个数组流，这样就可以去重了
     *  8 A I J L a b c d i m n o s t v
     */
}

Li peek times

And terminal operation, are circulated. Peek with the method, which receives a comsumer method. This method can best embody intermediate stateless operation:

//遍厉 peek
@Test
public void peekTest() {
    list.stream()
            //获取商品名称
            .map(Sku::getSkuName)
            //遍厉
            .peek(skuName -> System.out.println(skuName + " peek"))
            .forEach(System.out::println);
    /**
     * 看结果是和forEach效替进行输出，而不是peek输出之后再进行forEach
     * 说明，peek不用在所有的元素的基础上进行操作，只用消费就行了
     *
     * 无人机 peek
     * 无人机
     * VR一体机 peek
     * VR一体机
     * 纯色衬衫 peek
     * 纯色衬衫
     * 牛仔裤 peek
     * 牛仔裤
     * 跑步机 peek
     * 跑步机
     * Java编程思想 peek
     * Java编程思想
     * Java核心技术 peek
     * Java核心技术
     * 算法 peek
     * 算法
     * TensorFlow进阶指南 peek
     * TensorFlow进阶指南
     */
    list.stream()
            //获取商品名称
            .map(Sku::getSkuName)
            //遍厉
            .peek(skuName -> System.out.println(skuName + " peek"))
            //排序
            .sorted()
            .forEach(System.out::println);
    /**
     * 这个地方就是加了一个有状态中间操作
     * 因为排序必须在所有的数据基础上进行操作的
     * 
     * 无人机 peek
     * VR一体机 peek
     * 纯色衬衫 peek
     * 牛仔裤 peek
     * 跑步机 peek
     * Java编程思想 peek
     * Java核心技术 peek
     * 算法 peek
     * TensorFlow进阶指南 peek
     * Java核心技术
     * Java编程思想
     * TensorFlow进阶指南
     * VR一体机
     * 无人机
     * 牛仔裤
     * 算法
     * 纯色衬衫
     * 跑步机
     */
}

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