java8 的stream 测试练习

电玩女神 2022-02-04 01:17 202阅读 0赞

public static void main(String[] args) {
        List<UserModel> list=new ArrayList<UserModel>();
        UserModel userModel=new UserModel(1,"张三",new Date(System.currentTimeMillis()),"1110",1);
        UserModel userModel1=new UserModel(2,"李四",new Date(System.currentTimeMillis()),"1111",2);
        UserModel userModel2=new UserModel(3,"王五",new Date(System.currentTimeMillis()),"1112",2);
        UserModel userModel3=new UserModel(4,"小岛",new Date(System.currentTimeMillis()),"1113",2);
        list.add(userModel);
        list.add(userModel1);
        list.add(userModel2);
        list.add(userModel3);
    
        //通过list获取一个Int为key，List<object>为value 的map
        //Map<Integer,List<TmsTransportPlanItem>>
        Map<Integer, List<UserModel>> oneMap = list.stream().collect(Collectors.groupingBy(UserModel::getId));
        List<UserModel> models1 = oneMap.get(1);
    
    
        //list中获取id的list列表
        //List<Integer> cityIds
        //id返回list集合
        List<Integer> idList = list.stream().map(UserModel::getId).collect(Collectors.toList());
        //sex返回集合
        List<Integer> sexList = list.stream().map(UserModel::getSex).distinct().collect(Collectors.toList());
        //姓名list
        List<String> nameList = list.stream().map(UserModel::getName).collect(Collectors.toList());
    
    
        //获取list中不同的id字段。返回一个list<Integer>属性、
        List<Integer> newIdList = list.stream().map(UserModel::getId).collect(Collectors.toList());
    
    
        //根据条件从list中获取一个值，如果没有就直接返回null
        //TmsLogisticsOrder exit
        UserModel singleModel = list.stream().filter(item -> item.getSex() == 1).findAny().orElse(null);
    
    
        //获取list中的一个对象的字段返回set
        //Set<String> transOrderCodeSet
        Set<String> nameSet = list.stream().map(UserModel::getName).collect(Collectors.toSet());
    
    
        //把list<Ojbect>转成map<int,object>
        //Map<Integer, TmsTransportOrder> transOrderMap
        Map<Integer, UserModel> modelMap = list.stream().collect(Collectors.toMap(UserModel::getId, item -> item));
    
    
        //根据条件查找list中对应的值，返回一个list中的一个对象
        //TmsLogisticsOrderItem exitItem
        UserModel model = list.stream().filter(item -> "张三".equals(item.getName())).findAny().orElse(null);
        System.out.println(model);
    
    
        //获取list<object>中的一个字段，转换成int数组
        //Integer[] orderItemIds
        Integer[] arrayIds = list.stream().map(UserModel::getId).distinct().toArray(Integer[]::new);
        System.out.println(arrayIds);
    
    
        //获取map<int,List<object>>这样的集合。通过list<ojbect>来进行
        //Map<Integer,List<TmsLogisticsOrderItem>> logisticsOrderItemMap
        Map<Integer, List<UserModel>> listMap = list.stream().collect(Collectors.groupingBy(UserModel::getId));
        System.out.println(listMap);
    
    
        //获取int数组。通过list<object>
        //Integer[] orderIds
        Integer[] array = list.stream().map(UserModel::getId).distinct().toArray(Integer[]::new);
        System.out.println(array);
    
    
        //根据条件获取list<object>中的一个值，只要找到任何一个就可以。如果没有那么返回null
        //msLogisticsOrder exit
        List<UserModel> models = list.stream().filter(item -> item.getName().equals("李四")).collect(Collectors.toList());
        System.out.println(models);
    
    
        //通过list<object>获取set集合
        //Set<Integer> warehouseIdWithPermissionSet
        Set<Integer> integers = list.stream().map(UserModel::getId).distinct().collect(Collectors.toSet());
    
    
        //通过单个字符串转换成list进行查询
        String str = Collections.singletonList("张三").stream().filter(item -> item.equals("张三")).findFirst().get();
        System.out.println(str);
    
    
        //通过字符串（用逗号隔开的那种）返回一个list
        List<String> strings = Arrays.stream(("1,2,3,4,5,6,7,8,9").split(",")).collect(Collectors.toList());
        System.out.println(strings);
    
    
        //获取Map<Iint,Ojbect> 通过list<object>
        Map<Integer, UserModel> map = list.stream().collect(Collectors.toMap(UserModel::getId, item -> item));
        System.out.println(map);
    
    
        //获取Map<int,Ojbect> 通过list 但是要注意值的int转换
        //Map<Integer, AllocateDictionaryDTO> appStatusMap
        Map<Integer, UserModel> collectMap = list.stream().collect(Collectors.toMap(item -> Integer.parseInt(item.getStudentNo()), item -> item));
    
    
        System.out.println("");
    
    
    }