package com.wxrem.controller; import java.io.IOException; import java.nio.file.Files; import java.nio.file.Paths; import java.util.*; import java.util.stream.Collectors; import java.util.stream.Stream; /** * @author wxb * 操作的是一个数组可以使用Stream.of(1, 2, 3)方法将它转换为一个流。 * @date 2020-08-04 11:15 */ public class MyStreamTest { public static void main(String[] args) { ShopProperty p0 = new ShopProperty("叫了个鸡", 1000, 500, 2); ShopProperty p1 = new ShopProperty("叫了个鸡2", 1002, 100, 2); ShopProperty p2 = new ShopProperty("张三丰饺子馆", 2300, 1500, 3); ShopProperty p3 = new ShopProperty("永和大王", 580, 3000, 1); ShopProperty p4 = new ShopProperty("肯德基", 6000, 200, 4); List<ShopProperty> shopProperties = Arrays.asList(p0,p1,p2,p3,p4); // System.out.println(shopProperties); //筛选距离我最近的店铺 // getCloseShop(shopProperties); // getMapShop(shopProperties); // getFlatMap(); // getMaxPriceLevel(shopProperties); // getShopNameAndPriceLevel(shopProperties); getShopGroupByPriceLevel(shopProperties); } //参数和返回值不必属于同一种类型，但是lambda表达式必须是Function接口的一个实例 private static void getMapShop(List<ShopProperty> shopProperties) { Stream<Integer> integerStream = shopProperties.stream().map(shopProperty -> shopProperty.distance); System.out.println(integerStream.collect(Collectors.toList())); Stream<ShopProperty> shopPropertyStream = shopProperties.stream().map(shopProperty -> { Integer distance = shopProperty.distance; String name = shopProperty.name; ShopProperty s = new ShopProperty(name ,distance ,0,0); return s; }); System.out.println(shopPropertyStream.collect(Collectors.toList())); } //提取子流的操作，这种情况用的不多但是遇到flatMap将变得更容易处理。 private static void getFlatMap() { List<List<String>> lists = new ArrayList<>(); lists.add(Arrays.asList("apple", "click")); lists.add(Arrays.asList("boss", "dig", "qq", "vivo")); lists.add(Arrays.asList("c#", "biezhi")); List<String> collect = lists.stream().flatMap(Collection::stream) .filter(str -> str.length() == 2) .collect(Collectors.toList()); System.out.println(collect); } private static void getFlatMap2() { String[] words = new String[]{"Hello", "World"}; List<String> a = Arrays.stream(words) .map(word -> word.split("")) .flatMap(Arrays::stream) .distinct() .collect(Collectors.toList()); a.forEach(System.out::print); } private static void getCloseShop(List<ShopProperty> shopProperties) { String name1 = shopProperties.stream().sorted(Comparator.comparingLong(s -> s.distance)) .findFirst().get().name; System.out.println("距离我最近的店铺是:" + name1); Collections.sort(shopProperties, (x,y) -> x.distance.compareTo(y.distance)); String name2 = shopProperties.get(0).name; System.out.println("距离我最近的店铺是:" + name2); } // jdk7 提供方法 Files.readAllLines... 返回List<String> public static void getFileToList() { try { String readAllLines = Files.readAllLines(Paths.get("E:\\workspace\\github\\AllLinesFile.txt")) .stream().collect(Collectors.joining("\n")); System.out.println(readAllLines.toString()); }catch (IOException e){ e.printStackTrace(); } } //为了让Stream对象按照价格等级进行排序，需要传给它一个Comparator对象。 //Java8提供了一个新的静态方法comparingInt，使用它可以方便地实现一个比较器。 //放在以前，我们需要比较两个对象的某项属性的值，现在只需要提供一个存取方法就够了 public static void getMaxPriceLevel(List<ShopProperty> shopProperties){ Optional<ShopProperty> max = shopProperties.stream().max(Comparator.comparingInt(s -> s.priceLevel)); System.out.println(max.get()); } public static void getShopNameAndPriceLevel(List<ShopProperty> shopProperties){ Map<String, Integer> shopNameAndPriceLevel = shopProperties.stream(). collect(Collectors.toMap(ShopProperty::getName, ShopProperty::getPriceLevel)); System.out.println(shopNameAndPriceLevel); } //所有价格等级的店铺：类似group by public static void getShopGroupByPriceLevel(List<ShopProperty> shopProperties){ Map<Integer, List<ShopProperty>> getShopGroupByPriceLevel = shopProperties.stream(). collect(Collectors.groupingBy(ShopProperty::getPriceLevel)); System.out.println(getShopGroupByPriceLevel); } //Stream并行流 //流使得计算变得容易，它的操作也非常简单，但你需要遵守一些约定。默认情况下我们使用集合的stream方法 //创建的是一个串行流，你有两种办法让他变成并行流。 // //调用Stream对象的parallel方法 //创建流的时候调用parallelStream而不是stream方法 //我们来用具体的例子来解释串行和并行流 // 店铺属性 static class ShopProperty { String name; // 距离，单位:米 Integer distance; // 销量，月售 Integer sales; // 价格，这里简单起见就写一个级别代表价格段 Integer priceLevel; public ShopProperty(String name, int distance, int sales, int priceLevel) { this.name = name; this.distance = distance; this.sales = sales; this.priceLevel = priceLevel; } @Override public String toString() { return "ShopProperty{" + "name='" + name + '\'' + ", distance=" + distance + ", sales=" + sales + ", priceLevel=" + priceLevel + '}'; } public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getDistance() { return distance; } public void setDistance(Integer distance) { this.distance = distance; } public Integer getSales() { return sales; } public void setSales(Integer sales) { this.sales = sales; } public Integer getPriceLevel() { return priceLevel; } public void setPriceLevel(Integer priceLevel) { this.priceLevel = priceLevel; } } }
