Java集合排序
2021/12/1 17:37:00
本文主要是介绍Java集合排序,对大家解决编程问题具有一定的参考价值,需要的程序猿们随着小编来一起学习吧!
Java集合排序
List 集合
存储元素不为 null,且排序字段不为 null
public static void main(String[] args) { List<UserDTO> userDTO = new ArrayList<>(); userDTO.add(new UserDTO(new BigInteger("1"), "c", "s")); userDTO.add(new UserDTO(new BigInteger("2"), "d", "ss")); userDTO.add(new UserDTO(new BigInteger("3"), "a", "ss")); // 匿名内部类排序 Collections.sort(userDTO, new Comparator<UserDTO>() { @Override public int compare(UserDTO o1, UserDTO o2) { return o1.getUsername().compareTo(o2.getUsername()); } }); // 匿名内部类简化为 Lambda 排序 Collections.sort(userDTO, (UserDTO u1, UserDTO u2) -> u1.getUsername().compareTo(u2.getUsername())); // Java8中,List 类的 sort() 方法排序,简化为 userDTO.sort((UserDTO u1, UserDTO u2) -> u1.getUsername().compareTo(u2.getUsername())); // Java8 Lambda 类型推断简化排序 userDTO.sort((u1, u2) -> u1.getUsername().compareTo(u2.getUsername())); // 静态方法抽取公共 Lambda 表达式 userDTO.sort(UserDTO::compareByUsername); // Comparator 类 comparing() 方法,将 Function 参数作为比较元素 userDTO.sort(Comparator.comparing(UserDTO::getUsername)); // 多条件排序: Java8 使用 comparing()方法 和 thenComparing() 方法 userDTO.sort(Comparator.comparing(UserDTO::getUsername).thenComparing(UserDTO::getId)); // Java8 Stream sorted()排序 userDTO = userDTO.stream().sorted(Comparator.comparing(UserDTO::getUsername)).collect(Collectors.toList()); // 调转排序判断 倒序 userDTO.sort((u1, u2) -> u2.getUsername().compareTo(u1.getUsername())); // Comparator reversed() 方法倒序 Comparator<UserDTO> comparator = (u1, u2) -> u1.getUsername().compareTo(u2.getUsername()); userDTO.sort(comparator.reversed()); // Comparator comparing() 方法倒序 userDTO.sort(Comparator.comparing(UserDTO::getUsername, Comparator.reverseOrder())); // Stream Comparator.reverseOrder()倒序 userDTO.stream().sorted(Comparator.comparing(UserDTO::getUsername, Comparator.reverseOrder())).collect(Collectors.toList()); // 遍历打印 userDTO.forEach(userDTO1 -> System.out.println(userDTO1)); }
存储元素为 null,且排序字段不为 null
public static void main(String[] args) { List<UserDTO> userDTO = new ArrayList<>(); userDTO.add(new UserDTO(new BigInteger("1"), "c", "s")); userDTO.add(null); userDTO.add(new UserDTO(new BigInteger("2"), "d", "ss")); userDTO.add(new UserDTO(new BigInteger("3"), "a", "ss")); // Comparator.nullsLast() 排序,null 在结尾 集合存空对象,排序条件的字段不能为 null userDTO.sort(Comparator.nullsLast(Comparator.comparing(UserDTO::getUsername))); // Comparator.nullsFirst() 排序,null 在开头 集合存空对象,排序条件的字段不能为 null userDTO.sort(Comparator.nullsFirst(Comparator.comparing(UserDTO::getUsername))); // 遍历打印 userDTO.forEach(userDTO1 -> System.out.println(userDTO1)); }
存储元素为 null,且排序字段为 null
public static void main(String[] args) { List<UserDTO> userDTO = new ArrayList<>(); userDTO.add(new UserDTO(new BigInteger("1"), "c", "s")); userDTO.add(null); userDTO.add(new UserDTO(new BigInteger("2"), null, "ss")); userDTO.add(new UserDTO(new BigInteger("3"), "a", "ss")); // 排序条件的字段是 null,Comparator 组合 userDTO.sort(Comparator.nullsLast(Comparator.nullsLast(Comparator.comparing(UserDTO::getUsername, Comparator.nullsLast(String::compareTo))))); // 遍历打印 userDTO.forEach(userDTO1 -> System.out.println(userDTO1)); }
借鉴网址
使用 Lambda 表达式实现超强的排序功能(原创网址)
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