jdk1.8新特性集合部分

jdk1.8的stream用来处理集合，可以实现对集合的过滤，查找操作

　　集合排序sorted()

 List<Integer> aList = new ArrayList<>();
        aList.add(12);
        aList.add(14);
        aList.add(72);
        aList.add(42);
        aList.add(92);
        aList.add(22);
        aList.add(2);
        aList.add(10);
        aList.stream().sorted().forEach(a -> {
            System.out.println(a);
        });

　　

集合元素过滤 filter

 Stream<Integer> filter = aList.stream().filter(b -> b > 30);
        filter.sorted().forEach(c -> {
            System.out.println(c);
        });

　　

 

 集合数据去重distinct()，通过流中元素的 hashCode() 和 equals() 去除重复元素

 Stream<Integer> filter = aList.stream().distinct();
        filter.sorted().forEach(c -> {
            System.out.println("---去重后有序打印:" + c);
        });

　　

获取n个元素limit(n)

Stream<Integer> filter = aList.stream().sorted().limit(3);
        filter.forEach(c -> {
            System.out.println("---获取三个元素打印:" + c);
        });

　　

 

 将Stream类型转化为我们需要的集合类型

aList = filter.collect(Collectors.toList());

　　

 

 map接收一个函数作为参数，该函数会被应用到每个元素上，并将其映射成一个新的元素

 UmAndCustomerIdParam um=new UmAndCustomerIdParam();
        List<UmAndCustomerIdParam> paramList=new ArrayList<UmAndCustomerIdParam>();
        paramList.add(new UmAndCustomerIdParam("qiuxie002","a001"));
        paramList.add(new UmAndCustomerIdParam("qiuxie002","a002"));
        paramList.add(new UmAndCustomerIdParam("qiuxie002","a002"));
        paramList.add(new UmAndCustomerIdParam("qiuxie002","a002"));
        paramList.add(new UmAndCustomerIdParam("qiuxie002","a002"));
        paramList.add(new UmAndCustomerIdParam("qiuxie002","a002"));
        Set<String> collect = paramList.stream().map(UmAndCustomerIdParam::getOcmCustId).collect(Collectors.toSet());
        System.out.println(collect);

　　

 

 List<String> aList = dealStringList();
        List<String> collect = aList.stream().map(a -> a.replaceAll(",", "")).collect(Collectors.toList());
        collect.forEach(a -> {
            System.out.println(a);
        });

　　

 

 flatMap将每个值都转换成流

 List<String> aList = dealStringList();
        List<String> collect = aList.stream().flatMap(a -> {
            String[] split = a.split(",");
            Stream<String> stream = Arrays.stream(split);
            return stream;
        }).collect(Collectors.toList());
        System.out.println(collect);

　　

count 返回流中元素的总个数

List<Integer> queryList = queryList();
        long count = queryList.stream().count();
        System.out.println("集合中的元素数量:" + count);

　　

 

max 返回最大值

List<Integer> queryList = queryList();
        Integer integer = queryList.stream().max(Integer::compareTo).get();
        System.out.println("最大元素:" + integer);

　　

 

 min 返回最小值

 List<Integer> queryList = queryList();
        Integer integer = queryList.stream().min(Integer::compareTo).get();
        System.out.println("最小元素:" + integer);