"Actual or formal argument lists differs in length"

Question

When I try to put something in the () brackets of Friends f = new Friends(friendsName, friendsAge); it comes up with the error:

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.

But when I take out the arguments my friends list only displays "null 0". Are the values not set even though I have String friendsName = input.next();?

Also, when I try to remove a friend, it doesn't do anything. In the source code it does bring up a warning,

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

I'm confused on what that all means?

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;
    }
}

Solution 1

You try to instantiate an object of the Friends class like this:

Friends f = new Friends(friendsName, friendsAge);

The class does not have a constructor that takes parameters. You should either add the constructor, or create the object using the constructor that does exist and then use the set-methods. For example, instead of the above:

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

Solution 2

The default constructor has no arguments. You need to specify a constructor:

    public Friends( String firstName, String age) { ... }

Solution 3

Say you have defined your class like this:

    @Data
    @AllArgsConstructor(staticName = "of")
    private class Pair<P,Q> {

        public P first;
        public Q second;
    }

So when you will need to create a new instance, it will need to take the parameters and you will provide it like this as defined in the annotation.

Pair<Integer, String> pair = Pair.of(menuItemId, category);

If you define it like this, you will get the error asked for.

Pair<Integer, String> pair = new Pair(menuItemId, category);

Comments

[nanofarad]

You need to make a constructor for Friends(.

[resueman]

He actually does have some properties on it. They're just located above the getters/setters instead of at the top.

[user2585969]

Awesome. Thanks for the help! Do you have any idea why the "friendsList.remove(input.next());" isn't happy?

[PaulProgrammer]

You can't remove a String from a list that contains Friend objects. You'll have to iterate through the list of Friend and find the Friend that has the name the same as what was entered.

[PaulProgrammer]

Note that I consider the "empty constructor + modifiers" an anti-pattern. I don't think that it's a good idea to be able to construct objects that can't be used, or would cause errors or other surprises until they're initialized in subsequent (possibly forgotten) steps.

[Joni]

I'm not a fan either but they have their uses in certain types of programs (think java beans and dtos)

[JavaYouth]

I had a similar issue. But the constructor was there in another project that my project was dependent on. Eclipse did not complain but I got compile time on mvn install. I am wondering how this could be possible. Although I got it resolved using setters as mentioned in the accepted answer, I am just curious to know what was wrong.