Java 打印带有组名称的 ArrayList 组
我只是一个初学者，正在自学Java！我只有一个用户对象的数组列表：
class Users{
public userName;
public userNumber;
}
然后我创建一个模型：
ArrayList<Users> model=new ArrayList<Users>();
并将模型项添加为：
model.add(new Users("abc","123"));
model.add(new Users("def","888"));
model.add(new Users("abc","246"));
model.add(new Users("def","999"));
model.add(new Users("abc","456"));
我想要做的是以这种方式打印模型，该模型应显示类似的分组数据，其组名称如下：
for(int i=0;i:i<users.size;i++){
System.out.printlin("users:::"+users.get(i).userNumber);
}
但它也应该按名称分组和打印组，即：
abc ->
users:::123
users:::246
users:::456
def ->
users:::888
users:::999
所以我想对数据进行分组，然后以分组格式打印数据以及每个组名称！
我该怎么办，我正在自学Java。提前致谢
九州编程浏览 116回答 5
5回答
-
holdtom
public class User {private String userName;public String getUserName() { return userName;}public User(String userName, String userNumber) { this.userName = userName; this.userNumber = userNumber;}public void setUserName(String userName) { this.userName = userName;}public String getUserNumber() { return userNumber;}public void setUserNumber(String userPassword) { this.userNumber = userPassword;}private String userNumber;}主类import java.util.ArrayList;import java.util.HashMap;import java.util.List;public class MainMethod {private static HashMap<User, ArrayList<User>> maps;private static ArrayList<User> user1list;private static ArrayList<User> user2list;public static void main(String...args) { maps = new HashMap<>(); user1list = new ArrayList<>(); user2list = new ArrayList<>(); User user1 = new User("Ram", "1234"); User user2 = new User("Alish", "5678"); User user3 = new User("Ram", "91011"); User user4 = new User("Alish", "121314"); user1list.add(user1); user1list.add(user3); user2list.add(user2); user2list.add(user4); maps.put(user1, user1list ); maps.put(user2, user2list); /// User one lists for ( User userone: maps.get(user1)) { System.out.println("userone Name:::"+userone.getUserName()); System.out.println("User one Number:::"+userone.getUserNumber()); } System.out.println(); // USer tow list for (User usertwo: maps.get(user2)) { System.out.println("User two Name:::" +usertwo.getUserName()); System.out.println("User two Number :::" +usertwo.getUserNumber()); } } } -
烙印99
Map<String, List<Users>> use = model.stream.collect(Collectors.groupinBy(Person::getUsername)) ;您可以使用这种方法按组打印数据 -
潇湘沐
使用 Java Streams 尝试如下所示。//group by user nameMap<String, Set<String>> map = model.stream().collect( Collectors.groupingBy(Users::getUserName, Collectors.mapping(Users::getUserNumber, Collectors.toSet()) ) );System.out.println(map);确保在 Users 类中实现getter 方法getUserName()、getUserNumber() 。这里我假设userName和userNumber都是字符串类型的数据。 -
潇潇雨雨
完成您想要的操作的一种快速而简单的方法是使用HashMap. 哈希映射是键值集合，在您的情况下，您将创建一个HashMap<String, List<String>>存储username键和userNumber值列表的存储（因为您有多个值）。那么你的代码将更改如下：迭代您拥有的所有用户。如果usernamehashmap 中存在，则将其添加usernumber到其中。如果username不存在，则将其添加到哈希映射中，并将 用作usernumber其列表的第一个元素。最后，您将迭代哈希图，打印它所具有的键和值。 -
慕娘9325324
请尝试下面的代码 -public class Users {public String userName;public String userNumber;public Users(String userName, String userNumber) { this.userName = userName; this.userNumber = userNumber;}public String getUserName() { return userName;}public void setUserName(String userName) { this.userName = userName;}public String getUserNumber() { return userNumber;}public void setUserNumber(String userNumber) { this.userNumber = userNumber;}public static void main(String ar[]) { ArrayList<Users> model = new ArrayList<Users>(); model.add(new Users("abc", "123")); model.add(new Users("def", "888")); model.add(new Users("abc", "246")); model.add(new Users("def", "999")); model.add(new Users("abc", "456")); Map<String, Set<String>> map = model.stream().collect(Collectors.groupingBy(Users::getUserName, Collectors.mapping(Users::getUserNumber, Collectors.toSet()))); for (Map.Entry<String, Set<String>> entry : map.entrySet()) { Set set = entry.getValue(); Iterator value = set.iterator(); while (value.hasNext()) { System.out.println(entry.getKey() + " : " + value.next()); } }}}
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