[英]Custom HashMap by extending
Question: How do you create a custom HashMap class, extending HashMap, that can be manipulated like normal?
问题:如何创建自定义HashMap类,扩展HashMap,可以像平常一样进行操作?
Let me explain. 让我解释。 According to this question , you can create custom methods with ArrayLists by extending ArrayList and then writing your method.
根据这个问题 ,您可以通过扩展ArrayList然后编写方法来使用ArrayLists创建自定义方法。 How would I do that with HashMaps?
我怎么用HashMaps做到这一点?
I want to create a UserList class that can be initialized with UserList users = new HashMap<Users, Integer>
. 我想创建一个UserList类,可以使用
UserList users = new HashMap<Users, Integer>
进行初始化。 This is my class for UserList so far: 到目前为止,这是我的UserList类:
public class UserList extends HashMap<Users, Integer> {
public Users getUser(UUID uuid) {
for (Users u: keySet()) {
if (u.getUuid().equals(uuid))
return u;
}
return null;
}
public Boolean containsPlayer(UUID uuid) {
for (Users u: keySet()) {
if (u.getUuid().equals(uuid))
return true;
}
return false;
}
public Users removeUser(UUID uuid) {
for (Users u: keySet()) {
if (u.getUuid().equals(uuid)) {
remove(u);
return u;
}
}
return null;
}
}
But whenever I type private UserList listOfUsers = new HashMap<Users, Integer>;
但每当我键入私有
UserList listOfUsers = new HashMap<Users, Integer>;
in the main class, it brings up an incompatible type error. 在主类中,它会出现不兼容的类型错误。 How do I fix this?
我该如何解决? I remember learning about this before, but I've since forgotten.
我记得以前对此有所了解,但我已经忘记了。
Thanks 谢谢
UserList users = new UserList()
, no need for anything else. UserList users = new UserList()
,不需要任何其他内容。
By extending the HashMap
you already told the compiler that UserList
is a HashMap
. 通过扩展
HashMap
您已经告诉编译器UserList
是HashMap
。
As a suggestion, you may want to consider composition as an alternative design: Composition over inharitance 作为建议,您可能希望将构图视为一种替代设计: 构图而不是吸入
I know your question is about extending HashMap, but you can achieve the same by encapsulating the HashMap implementation inside your object: 我知道你的问题是关于扩展HashMap,但你可以通过在对象中封装HashMap实现来实现同样的目的:
import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
public class UserList {
private Map<UUID, Users> users;
public UserList() {
this.users = new HashMap<>();
}
public Users getUser(UUID uuid) {
return this.users.getOrDefault(uuid, null);
}
public Users removeUser(UUID uuui){
return this.users.remove(uuui);
}
public Boolean containsPlayer(UUID uuid) {
return this.users.keySet().contains(uuid);
}
public Users addUser(UUID uuid, Users users) {
return this.users.put(uuid, users);
}
}
class Users{}
class Main{
public static void main(String[] args) {
UserList userList = new UserList();
UUID uuid = UUID.randomUUID();
Users users = new Users();
userList.addUser(uuid, users);
userList.removeUser(uuid);
userList.containsPlayer(uuid);
}
}
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