Java8 函数式编程 lambda 方法引用 Stream流
Stream Java8新增的一个接口，以声明性方式处理数据集合
流水线
数据源+零或者多个中间操作+一个终端操作


Stream特点
只能遍历（消费）一次
保护数据源
lazy 中间运算 filter map  , 终端操作（如collect）



Stream 创建

Stream strStream = Stream.of("hello", "java8", "stream");
		
IntStream intStream = IntStream.of(1, 2, 3);
		
List intList = Arrays.asList(4,5,6);
Stream integerStream = intList.stream();

Integer[] array = {7, 8, 9};
integerStream = Arrays.stream(array);

Random random = new Random();		
intStream = random.ints().limit(3);
		
integerStream = Stream.generate(random::nextInt).limit(3);

// 生成3个奇数
integerStream = Stream.iterate(1, n -> n + 2).limit(3);
		
Stream pathStream = Files.list(Paths.get("/"));





Stream常用操作

两类操作

中间操作 filter map  等 
终端操作 foreach min  max count  collect 等


		List words = Arrays.asList("hello", "java8", "stream");
		// 计算每个单词的长度
		List list = words.stream().map(String::length).collect(Collectors.toList());
		// 5 5 6
		list.forEach(System.out::println);
		
		words = Arrays.asList("a", "b-c", "d-e-f");
		List list1 = words.stream().map(word -> word.split("-")).collect(Collectors.toList());
		list1.forEach(System.out::println);

		
		Stream strStream2 = words.stream().map(word -> word.split("-")).flatMap(Arrays::stream).distinct();
		strStream2.forEach(System.out::println);


		List words2 = Arrays.asList("hello", "java8", "stream");

		words2.stream()
        .filter(word -> word.length() > 5)
        .collect(Collectors.toList())
        .forEach(System.out::println);


		List integers = Arrays.asList(7, 9, 8);
		integers.stream().max(Integer::compareTo).ifPresent(System.out::println);
		
		


常见错误

重复使用流

		Stream strStream3 = Stream.of("hello", "java8", "stream");
		strStream3.forEach(System.out::println);
		//  java.lang.IllegalStateException: stream has already been operated upon or closed
		try {
		    strStream3.forEach(System.out::println);
		}catch(Exception e) {
			System.out.println(e);
		}

修改数据源	
		List strings = Arrays.asList("hello", "java8", "stream");
		
		// java.lang.UnsupportedOperationException	
		strings.stream()
		        .map(s -> {
		            strings.add("world");
		            return s.toUpperCase();
		        }).forEach(System.out::println);



完整代码
https://gitee.com/dyyx/hellocode/blob/master/src/dyyx/java8/StreamTest4.java


 JAVA8 stream 集合处理