stream().filter()的用法

• stream.filter一般适用于list集合,主要作用就是模拟sql查询，从集合中查询想要的数据。filter里面的参数user是指集合里面的每一项

  public class StreamTest{
      public static void main(String[] args){
          List<User> list = new ArrayList<>();
          //定义三个用户对象
          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");
          //添加用户到集合中
          list.add(user1);
          list.add(user2);
          list.add(user3);
  ​
          //在集合中查询用户名为huxiansen的集合
          List<User> userList = list.stream().filter(user -> "huxiansen".equals(user.getUsername())).collect(Collectors.toList());
          //在集合中查询出第一个用户密码为123456的用户
          Optional<User> user = list.stream().filter(userTemp -> "123456".equals(userTemp.getPassword())).findFirst();
  ​
          System.out.println(userList);
          System.out.println(user);
      }
  }

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