java 8 stream流学习笔记

public class StreamTest {

    public static void main(String[] args)  {
        Random random = new Random();
        System.out.println("===使用forEach打印5个随机数并排序===");
        random.ints().limit(5).sorted().forEach(System.out::println);
        System.out.println("========================================");

        List<Integer> numbers = Arrays.asList(9,1,2,3,7,8,5);
        System.out.println("===使用sorted降序排列====默认升序===");
        List<Integer> sortedList = numbers.stream().sorted(Comparator.comparingInt(Integer::intValue).reversed()).collect(Collectors.toList());
        System.out.println(sortedList);
        System.out.println("========================================");

        System.out.println("===使用map将计算元素的结果映射到结果集===");
        List<Integer> squaresList = numbers.stream().map(i -> i*(i+1)).collect(Collectors.toList());
        System.out.println(squaresList);
        System.out.println("========================================");


        List<String> strList = Arrays.asList("asd","","dgf","","fghh","asd","dgf");

        System.out.println("===使用filter将List中不为空的元素放到另一个List中====");
        List<String> filterList = strList.stream().filter(s -> !s.isEmpty()).collect(Collectors.toList());
        System.out.println(filterList);
        System.out.println("========================================");


        System.out.println("===使用filter将List中不为空的元素放到String中以“；”分割====");
        String filterString = strList.stream().filter(s -> !s.isEmpty()).collect(Collectors.joining(";"));
        System.out.println(filterString);
        System.out.println("========================================");

        System.out.println("===使用filter计算List中元素相同的个数====");
        Map<String,Integer> map=new HashMap<>();
        for (String str:
             strList) {
            int count = (int) strList.stream().filter(s -> s.equals(str)).count();
            if(!map.containsKey(str)&&!"".equals(str)){
                map.put(str,count);
            }else{
                map.put("空字符",count);
            }

        }
        Set<Map.Entry<String,Integer>> entry = map.entrySet();
        Iterator<Map.Entry<String,Integer>> iterator = entry.iterator();
        while(iterator.hasNext()){
            Map.Entry<String,Integer> next = iterator.next();
            System.out.println(next);
        }
        System.out.println("========================================");
    }
}

打印结果如下：