// 1.單列集合創(chuàng)建stream流
        List<String> list = Arrays.asList("張三", "李四", "王五", "趙六", "錢七");
        list.stream().forEach(e -> System.out.println("e = " + e));

        // 2.雙列集合創(chuàng)建stream流
        HashMap<String, Integer> map = new HashMap<>();
        map.put("aaa", 111);
        map.put("bbb", 222);
        map.put("ccc", 333);
        map.put("ddd", 444);
        map.put("eee", 555);
        // 遍歷所有的key
        map.keySet().stream().forEach(e -> System.out.println("e = " + e));
        // 遍歷所有的鍵值對(duì)
        map.entrySet().stream().forEach(e -> System.out.println("e = " + e));
        // 遍歷所有的值
        map.values().stream().forEach(e -> System.out.println("e = " + e));

        // 3.數(shù)組創(chuàng)建stream流
        int[] array1 = {1, 2, 3};
        String[] array2 = {"a", "b", "c"};
        Arrays.stream(array1).forEach(e -> System.out.println("e = " + e));

     // 4.零散數(shù)據(jù)創(chuàng)建stream流
        Stream.of(1, 2, 3, 4, 5).forEach(e -> System.out.println("e = " + e));
        // stream接口中靜態(tài)方法of的細(xì)節(jié)
        // 方法的形參是一個(gè)可變參數(shù)，可以傳遞一堆零散的數(shù)據(jù)（同一類型），也可以傳遞數(shù)組
        // 傳遞的數(shù)組必須是引用數(shù)據(jù)類型的，如果傳遞基本數(shù)據(jù)類型，會(huì)把數(shù)組當(dāng)做一個(gè)元素
        Stream.of(array1).forEach(e -> System.out.println("e = " + e));  // 結(jié)果[I@4dd8dc3
        Stream.of(array2).forEach(e -> System.out.println("e = " + e));

     // 5.創(chuàng)建并行流
        list.parallelStream().forEach(e -> System.out.println("e = " + e)); // 順序會(huì)打亂

     // 6.創(chuàng)建無限流
        Stream.generate(Math::random).limit(10).forEach(e -> System.out.println("e = " + e));
        Stream.iterate(0, n -> n + 2).limit(10).forEach(e -> System.out.println("e = " + e));

       // 1.過濾操作
        // filter: 過濾元素
        List<Integer> list1 = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 100, 100);
        List<Integer> list2 = Arrays.asList(100, 200, 30, 40, 50, 60, 70, 80, 90, 100, 200, 1000, 100000);
        list1.stream().filter(n -> n % 2 == 0).forEach(e -> System.out.println("e = " + e));
        // distinct: 去重
        // 依賴于hashCode和equals方法，底層使用的是hashset
        list1.stream().distinct().forEach(e -> System.out.println("e = " + e));

     // 2.映射操作
        List<String> list3 = Arrays.asList("張三-13", "李四-14", "王五-15", "趙六-16", "錢七-17");
        list3.stream().map(s -> Integer.valueOf(s.split("-")[1])).forEach(e -> System.out.println("map = " + e));
         List<List<Integer>> numberLists = Arrays.asList(
                Arrays.asList(1, 2),
                Arrays.asList(3, 4, 5),
                Arrays.asList(6)
        );
        // flatMap 可以處理嵌套集合或需要"展平"數(shù)據(jù)結(jié)構(gòu)的情況，將每個(gè)元素轉(zhuǎn)換為一個(gè)流(Stream)，然后把所有流合并成一個(gè)流
        // 當(dāng)你需要處理嵌套結(jié)構(gòu)或一對(duì)多轉(zhuǎn)換時(shí)，使用flatMap；當(dāng)只是簡(jiǎn)單的一對(duì)一轉(zhuǎn)換時(shí)，使用map
        numberLists.stream().map(s -> s.stream()).forEach(stream -> System.out.println("stream = " + stream));  // 輸出3個(gè)流對(duì)象的地址值 java.util.stream.ReferencePipeline$Head@3b9a45b3
        numberLists.stream().flatMap(s -> s.stream()).forEach(s -> System.out.println("flatMap = " + s)); // 輸出 1 2 3 4 5 6

      // 3.截取/跳過操作
        // limit: 限制元素?cái)?shù)量
        list1.stream().limit(4).forEach(e -> System.out.println("e = " + e));
        // skip: 跳過前N個(gè)元素
        list1.stream().skip(5).forEach(e -> System.out.println("e = " + e));

      // 4.排序操作
        // sorted: 排序
        Stream.of("b", "a", "c").sorted().forEach(s -> System.out.println("sorted = " + s));
        // 自定義排序
        Stream.of("aaa", "bb", "c").sorted(Comparator.comparingInt(String::length)).forEach(s -> System.out.println("customSorted  = " + s));
        Stream.of("aaa", "bb", "c", null).sorted((a, b) -> {
            if (a == null && b == null) return 0;
            if (a == null) return 1;
            if (b == null) return -1;
            return b.compareTo(a);
        }).forEach(s -> System.out.println("customSorted2  = " + s));

      // 5.合并操作
        Stream.concat(list1.stream(), list2.stream()).forEach(e -> System.out.println("e = " + e));

      // 6.其他中間操作
        // peek: 查看流中元素，調(diào)試用
        Stream.of("one", "two", "three")
                .peek(e -> System.out.println("Original: " + e))
                .map(String::toUpperCase)
                .peek(e -> System.out.println("Mapped: " + e))
                .forEach(e-> System.out.println("peek = " + e));

     // 1.遍歷操作
        List<String> list = Arrays.asList("張三-13", "李四-14", "王五-15", "趙六-16", "錢七-17", "張三-23");
        // forEach: 遍歷元素
        list.stream().forEach(e -> System.out.println("e = " + e));
        // forEachOrdered: 保證順序的遍歷
        list.parallelStream().forEachOrdered(e -> System.out.println("e = " + e));

      // 2.收集操作
        // 收集到list集合
        List<String> nameList = list.stream().map(e -> e.split("-")[0]).collect(Collectors.toList());
        System.out.println("nameList = " + nameList);
        // 收集到set集合，會(huì)去重
        Set<String> nameSet = list.stream().map(e -> e.split("-")[0]).collect(Collectors.toSet());
        System.out.println("nameSet = " + nameSet);
        // 收集到map集合
        // 注意收集到map，鍵不能重復(fù)，重復(fù)會(huì)報(bào) java.lang.IllegalStateException: Duplicate key 張三 (attempted merging values 13 and 23)
//        Map<String, Integer> map1 = list.stream().collect(Collectors.toMap(s -> s.split("-")[0], s -> Integer.valueOf(s.split("-")[1])));
//        System.out.println("map1 = " + map1);
        // 解決方案，傳遞第三個(gè)參數(shù)，如果鍵重復(fù)，使用前面的那么，以下的(a, b)代表的value，a為已經(jīng)存在的，b為新加的
        Map<String, Integer> map2 = list.stream().collect(Collectors.toMap(s -> s.split("-")[0], s -> Integer.valueOf(s.split("-")[1]), (a, b) -> a));
        System.out.println("map2 = " + map2);
        // 收集為字符串
        String nameStr = list.stream().map(e -> e.split("-")[0]).collect(Collectors.joining("-"));
        System.out.println("nameStr = " + nameStr);   // 張三-李四-王五-趙六-錢七-張三

     // 3.聚合操作
        // count: 計(jì)數(shù)
        long count = Stream.of("a", "b", "c").count();
        System.out.println("count = " + count); // 3
        // max/min: 最大最小值
        Optional<String> max = Stream.of("a", "bb", "ccc").max(Comparator.comparingInt(String::length));
        System.out.println("max = " + max.get());
        // reduce: 歸約操作
        // 無初始值，當(dāng)流為空，則為Optional.empty()
        Optional<Integer> sum = Stream.of(1, 2, 3).reduce(Integer::sum);
        System.out.println("sum = " + sum.get()); // ccc
        // 初始值為0，流為空則返回0，執(zhí)行的操作為 0+1+2+3 = 6
        Integer sumWithIdentity = Stream.of(1, 2, 3).reduce(0, Integer::sum);
        System.out.println("sumWithIdentity = " + sumWithIdentity); // 6

       // 4.匹配操作
        // anyMatch: 任意元素匹配(任意一個(gè)滿足條件則為true)
        boolean hasEven = Stream.of(1, 2, 3).anyMatch(n -> n % 2 == 0);
        System.out.println("hasEven = " + hasEven); // true
        // allMatch: 所有元素匹配(所有元素都要滿足條件)
        boolean allEven = Stream.of(2, 4, 6).allMatch(n -> n % 2 == 0);
        System.out.println("allEven = " + allEven); // true
        // noneMatch: 沒有元素匹配(所有元素都不能滿足條件)
        boolean noneNegative = Stream.of(1, 2, 3).noneMatch(n -> n < 0);
        System.out.println("noneNegative = " + noneNegative); // true

      // 5.查找操作
        // findFirst: 查找第一個(gè)元素
        Optional<String> first = Stream.of("a", "b", "c").findFirst();
        System.out.println("first = " + first.get()); // a
        // findAny: 查找任意元素(在并行流中效率更高)
        Optional<String> any = Stream.of("a", "b", "c").parallel().findAny();
        System.out.println("any = " + any.get()); // b

        // 6.數(shù)組轉(zhuǎn)換
        // toArray: 轉(zhuǎn)換為數(shù)組
        String[] array = Stream.of("a", "b", "c").toArray(String[]::new);
        System.out.println("array = " + Arrays.toString(array)); // [a, b, c]

        // 7.分組
        // 可將一個(gè)對(duì)象集合按照里面的某個(gè)字段轉(zhuǎn)換為map，如key為ID，value為對(duì)象
        List<String> words = Arrays.asList("apple", "banana", "orange", "pear", "grape");
        Map<Integer, List<String>> groupedByLength = words.stream()
                .collect(Collectors.groupingBy(String::length));
        System.out.println(groupedByLength);