java - "Actual or formal argument lists differs in length"

Question

当我尝试在 Friends f = new Friends(friendsName, friendsAge); 的 () 括号中添加内容时出现错误:

Constructor Friends in class Friends cannot by applied to given types. Required: no arguments. Found: String, int. Reason: actual or formal argument lists differ in length.

但是当我取出参数时，我的 friend 列表只显示“null 0”。即使我有 String friendsName = input.next();，是否还没有设置值？

此外，当我尝试删除好友时，它没有任何作用。在源代码中它确实提出了一个警告，

Suspicious call to util.java.Collection.remove: Given object cannot contain given instances of String (expected Friends).

我对这一切的含义感到困惑？

import java.util.ArrayList;
import java.util.Scanner;

public class Friends
{
    public static void main( String[] args )
    {
        int menu;       
        int choice;
        choice = 0;      

        Scanner input = new Scanner(System.in);
        ArrayList< Friends > friendsList = new ArrayList<  >();       

        System.out.println(" 1. Add a Friend ");
        System.out.println(" 2. Remove a Friend ");
        System.out.println(" 3. Display All Friends ");
        System.out.println(" 4. Exit ");
        menu = input.nextInt();

        while(menu != 4)
        {    

            switch(menu)
            {                     

            case 1:

                while(choice != 2)
                {
                    System.out.println("Enter Friend's Name: ");
                    String friendsName = input.next();
                    System.out.println("Enter Friend's Age: ");
                    int friendsAge = input.nextInt();                               
                    Friends f = new Friends(friendsName, friendsAge);
                    friendsList.add(f);
                    System.out.println("Enter another? 1: Yes, 2: No");
                    choice = input.nextInt();
                } break;

            case 2:

                System.out.println("Enter Friend's Name to Remove: ");
                friendsList.remove(input.next());                   
                break;   

            case 3:

                for(int i = 0; i < friendsList.size(); i++)
                {
                    System.out.println(friendsList.get(i).name + " " + friendsList.get(i).age);                        
                } break;                
        }

        System.out.println(" 1. Add a Friend ");
        System.out.println(" 2. Remove a Friend ");
        System.out.println(" 3. Display All Friends ");
        System.out.println(" 4. Exit ");
        menu = input.nextInt();

    }

    System.out.println("Thank you and goodbye!");

}

    public String name;
    public int age;    

    public void setName( String friendsName )
    {
        name = friendsName;
    } 
    public void setAge( int friendsAge )
    {
        age = friendsAge;
    }
    public String getName()
    {
        return name;
    }
    public int getAge()
    {
        return age;
    }
}

Answer 1

您尝试像这样实例化 Friends 类的对象:

Friends f = new Friends(friendsName, friendsAge);

该类没有带参数的构造函数。您应该添加构造函数，或者使用确实存在的构造函数创建对象，然后使用设置方法。例如，代替上面的:

Friends f = new Friends();
f.setName(friendsName);
f.setAge(friendsAge);