一、遍历与统计
java"> // forEach遍历ArrayList<String> list1 = new ArrayList<>();Collections.addAll(list1, "张无忌", "张三A", "张三B", "张三C","周五", "李四", "赵本三");list1.stream().forEach(System.out::println);// count 统计Long num = list1.stream().count();System.out.println(num);// toArray 收集变成数组String[] str = list1.stream().toArray(value -> new String[value]);System.out.println(Arrays.toString(str));二、Stream的常见方法
1、filter 过滤，limit获取前几个元素，skip跳过前几个元素
java"> ArrayList<String> list1 = new ArrayList<>();Collections.addAll(list1, "张无忌", "张三A", "张三B", "张三C","周五", "李四", "赵本三");// 需求：张开头，最大数量为3，跳过第一个，打印list1.stream().filter(s -> s.startsWith("张")) //张开头.limit(3) // 最大数量为3.skip(1) //跳过第一个.forEach(System.out::println);/*结果：张三A张三B*/2、map 转化流转的两种数据类型
java"> ArrayList<String> list1 = new ArrayList<>();Collections.addAll(list1, "张无忌-1", "张三A-2","张三B-3", "张三C-4","周五-5", "李四-6", "赵本三-7");System.out.println(list1);// 字符串转为整型list1.stream().map(s -> Integer.parseInt(s.split("-")[1])).forEach(s-> System.out.print(s + " "));
3、distinct去重
java">ArrayList<String> list1 = new ArrayList<>();Collections.addAll(list1, "张无忌", "张无忌", "张无忌", "张三C","周五", "李四", "赵本三");list1.stream().distinct().forEach(System.out::println);4、concat 合并两个流
java">ArrayList<String> list1 = new ArrayList<>();Collections.addAll(list1, "a","b","c");ArrayList<String> list2 = new ArrayList<>();Collections.addAll(list2, "d","e","f");Stream.concat(list1.stream(),list2.stream()).forEach(System.out::println);三、Stream的收集
使用Java的Stream API对一个包含字母-性别-编号格式字符串的ArrayList进行处理：首先通过filter筛选出性别为“男”的元素，分别收集到List和Set中；然后通过toMap将每个字符串的字母作为键、编号作为值，收集到Map中，最终实现了对数据的分类和转换。
java">ArrayList<String> list = new ArrayList<>();Collections.addAll(list, "A-男-01", "B-男-02", "C-男-03","D-男-04", "E-女-05","F-女-06", "G-男-07");// 需求一：用list把男生收集起来List<String> list1 = list.stream().filter(s -> "男".equals(s.split("-")[1])).collect(Collectors.toList());System.out.println(list1);// 需求二：用set把男生收集起来Set<String> list2 = list.stream().filter(s -> "男".equals(s.split("-")[1])).collect(Collectors.toSet());System.out.println(list2);// 需求三：用map收集所有信息，字母对应编号// ps：map收集不能有两个键相同Map<String, Integer> map = list.stream().collect(Collectors.toMap(s -> s.split("-")[0],s -> Integer.parseInt(s.split("-")[2])));System.out.println(map);
