java 无法推断 ArrayList<> 的类型参数
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cannot infer type arguments for ArrayList<>
提问by mg22
I'm trying to make an ArrayList that contains an object of another class, a name, and turn. something similar to the python's dictionary.
我正在尝试创建一个包含另一个类的对象、名称和轮次的 ArrayList。类似于python的字典的东西。
self.user1 = {"user":user1,"name":empty,"turn":empty}
so I made a class that has the 3 values.
所以我做了一个具有 3 个值的类。
class User{
public userInterface user1;
String name;
String turn;
public User(UserInterface user1,String name,String turn) {
this.user1=user1;
this.name=name;
this.turn=turn;
}}
and I'm trying to call it in the constructor of main class as following:
我试图在主类的构造函数中调用它，如下所示：
public class MainClassConstructon{
ArrayList<User> user1;
ArrayList<User> user2;
MainClassConstructon(UserInterface user1 ,UserInterface user2){
this.user1 = new ArrayList<>(new User(user1,empty, empty));
this.user2 = new ArrayList<>(new User(user2,empty, empty));
but it raises an error saying that: cannot infer type arguments for ArrayList<>.
但它引发了一个错误，指出：无法推断 ArrayList<> 的类型参数。
回答by Jeroen Steenbeeke
ArrayList has three constructors:
ArrayList 有三个构造函数：
public ArrayList(int initialCapacity)
public ArrayList()
public ArrayList(Collection<? extends E> c)
Useris neither an intnor a Collection, and you're passing an argument so the middle constructor doesn't apply either.
User既不是 anint也不是 a Collection，并且您正在传递一个参数，因此中间构造函数也不适用。
But that's beside the point, your goal is to create a single list of users, so instead of doing what you're currently doing, you need to use only a single list, and simply add your users:
但这不是重点，您的目标是创建一个用户列表，因此您无需执行当前正在执行的操作，只需使用一个列表，然后添加您的用户即可：
public class MainClassConstructon{
List<User> users; // Or ArrayList, doesn't really matter
MainClassConstructon(UserInterface user1 ,UserInterface user2){
users = new ArrayList<>(); // Diamond syntax, requires Java 7+
users.add(new User(user1, "", ""));
users.add(new User(user2, "", ""));
}
}
回答by mg22
well i made it like this:
好吧，我是这样制作的：
this.user1 = new ArrayList<>(Arrays.asList(new User(user1,empty, empty)));
and was able to access it by:
并且能够通过以下方式访问它：
t.user1.get(0).name="bla bla";
回答by ckoidl
you can try it like this
你可以这样试试
public class MainClassConstructon {
ArrayList<User> user1 = new ArrayList<>();
ArrayList<User> user2 = new ArrayList<>();
MainClassConstructon(UserInterface user1, UserInterface user2) {
this.user1.add(new User(user1, "", ""));
this.user2.add(new User(user2, "", ""));
}
}
回答by Daniel Arad
I'm not a java developer but i suggest you try and look on Arraylist api.
我不是 Java 开发人员，但我建议您尝试查看 Arraylist api。
Here is what i found online, sry if it doesn't help :)
这是我在网上找到的，如果没有帮助，请sry :)
import java.util.*;
public class ArrayListDemo { public static void main(String args[]) {
// create an array list
ArrayList al = new ArrayList();
System.out.println("Initial size of al: " + al.size());
// add elements to the array list
al.add("C");
al.add("A");
al.add("E");
al.add("B");
al.add("D");
al.add("F");
al.add(1, "A2");
System.out.println("Size of al after additions: " + al.size());
// display the array list System.out.println("Contents of al: " + al);
// Remove elements from the array list al.remove("F");
al.remove(2);
System.out.println("Size of al after deletions: " + al.size());
System.out.println("Contents of al: " + al);
}
}
