利用Lambda处理集合常用方法

list转为Map

Map<String,User> userMap = list.stream().collect(Collectors.toMap(User::getName, a -> a,(k1, k2)->k1));
        System.out.println(userMap);

foreach循环

        User user=new User();
        user.setName("good");
        user.setAddr("dd");
        User user2=new User();
        user2.setName("goodbye");
        user2.setAddr("dda");
        List<User> list=new ArrayList<>();
        list.add(user);
        list.add(user2);
        list.stream().forEach(userObj->{
            System.out.println(userObj.getName());
        });

将List分组：List里面的对象元素，以某个属性来分组

Map<String, List<User>> groupBy = list.stream().collect(Collectors.groupingBy(User::getName));
        System.out.println(groupBy);

过滤：从集合中过滤出来符合条件的元素

List<User> filterList = list.stream().filter(user3 -> user3.getName().equals("good")).collect(Collectors.toList());
        filterList.stream().forEach(user3 ->{
            System.out.println(user3.getName());
        });

List中对象属性值作为 Map的ke和value

Map<String,String> userMap2 = list.stream().collect(Collectors.toMap(User::getName, User::getAddr,(k1, k2)->k1));
        System.out.println(userMap2);