stream().filter()的用法

stream.filter一般適用於list集合,主要作用就是模擬sql查詢，從集合中查詢想要的數據。filter里面的參數user是指集合里面的每一項

public class StreamTest{
    public static void main(String[] args){
        List<User> list = new ArrayList<>();
        //定義三個用戶對象
        User user1 = new User();
        user1.setUsername("huxiansen");
        user1.setPassword("123456");
        User user2 = new User();
        user2.setUsername("huxianseng");
        user2.setPassword("123456");
        User user3 = new User();
        user3.setUsername("huxiansen");
        user3.setPassword("12345");
        //添加用戶到集合中
        list.add(user1);
        list.add(user2);
        list.add(user3);
​
        //在集合中查詢用戶名為huxiansen的集合
        List<User> userList = list.stream().filter(user -> "huxiansen".equals(user.getUsername())).collect(Collectors.toList());
        //在集合中查詢出第一個用戶密碼為123456的用戶
        Optional<User> user = list.stream().filter(userTemp -> "123456".equals(userTemp.getPassword())).findFirst();
​
        System.out.println(userList);
        System.out.println(user);
    }
}