java 8 新特性
for (Map.Entry<String, String> entry : map.entrySet()) { String k = entry.getKey(); String v = entry.getValue(); System.out.println(k + " : " + v); }
JAVA8新特性之List的各种用法(最大、最小、平均值、分组、求和、遍历、过滤、排序)
https://www.cnblogs.com/Kevin-ZhangCG/p/14918181.html
//day 为user的一个属性 去重
List<User> setList = eachUser.stream()
.collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(User::getDay))), ArrayList::new));
原文链接:https://blog.csdn.net/xiaohanguo_xiao/article/details/105656411
例如说:(“s1”, 1, 1),(“s1”,2,3),(“s2”,4,4), 求和并去重的话,就是(“s1”, 3, 4),(“s2”,4,4)
List<OrderLine> orderLines = param.getOrderLine();
//合并sku数量
orderLines = new ArrayList<>(orderLines.stream()
// 表示id为key, 接着如果有重复的,那么从BillsNums对象o1与o2中筛选出一个,这里选择o1,
// 并把id重复,需要将nums和sums与o1进行合并的o2, 赋值给o1,最后返回o1
.collect(Collectors.toMap(OrderLine::getProductId, a -> a, (o1, o2) -> {
double qty = o1.getQuantity() ==null ? 0.0: o1.getQuantity();
double qty2 = o2.getQuantity() ==null ? 0.0: o2.getQuantity();
o1.setQuantity(qty + qty2);
return o1;
})).values());
参考:https://blog.csdn.net/qq_42928918/article/details/109763353
1. 分组 Map<String, List<SendDetail>> collect = details.stream().collect(Collectors.groupingBy(SendDetail::getCustomerId));
Map<String,WmHeader> map = headerList.stream().collect(Collectors.toMap(item -> String.join("_",item.getWareNo(),item.getLogNo()),item -> item, (k1, k2) -> k1));
Map<String, List<InvDetail>> listMap = invDetails.stream().collect(Collectors.groupingBy(lotLoc -> String.join("_",lotLoc.getCode() ,lotLoc.getTrId())));
List<Integer> ids = details.stream().map(SmsCustomerSendDetail::getId).collect(Collectors.toList());
//筛选出年龄大于3岁小于8岁的对象 List<Users> collect = list.stream().filter(s -> s.getAge() > 13 && s.getAge() < 18).collect(Collectors.toList());
List<String> collect = numList.stream().distinct().collect(Collectors.toList());
2. 单列求和 int totalValue = details.stream().mapToInt(SendDetail::getSmsFee).sum();
3. 提取单列数据集合 List<Integer> ids = details.stream().map(SendDetail::getId).collect(Collectors.toList());
作者:hisenyuan 链接:https://www.jianshu.com/p/c71eaeaaf30c
List<User> userList = new ArrayList<>(); userList.add(new User(1L, "zhangsan", 23, new BigDecimal(55))); userList.add(new User(2L, "lisi", 33, new BigDecimal(22))); userList.add(new User(3L, "wangwu", 44, new BigDecimal(44))); userList.add(new User(4L, "mazi", null, new BigDecimal(44))); // 对年龄进行统计 int ageCount = userList.stream() .mapToInt(item -> item.getAge() == null ? 0 : item.getAge()) .sum(); System.out.println("年龄总和: " + ageCount); //对资产进行统计 BigDecimal amounts1 = userList .stream() .map(item -> item.getAmount() == null ? BigDecimal.ZERO : item.getAmount()) .reduce(BigDecimal.ZERO, BigDecimal::add); System.out.println("资产总和1 :" + amounts1); ———————————————— 原文链接:https://blog.csdn.net/qq_35098526/article/details/88186797