I have 3 java source files.
Person.javaFriendsList.javaMyFriends.javaFriendsList contains an array list of objects of type Person and a method for adding a new friend to the list.
public class FriendsList{
ArrayList<Person> friendsList = new ArrayList<Person>(100);
// Constructor declaration of class
public FriendsList(ArrayList<Person> friendsList){
super();
this.friendsList = friendsList;
}
...
public void addFriend(Person friend){
friendsList.add(friend);
}
...
}
Now, in MyFriends.java I created a new array list of objects of type Person, I declared a new Person and I'm trying to add it to the list using the method addFriend(Person) but I'm getting an error "Method addFriend(Person) is undefined for the type ArrayList<Person>"
public class MyFriends{
public void main(String[] args){
ArrayList<Person> friendsList = new ArrayList<Person>(100);
Person f1 = new Person("Alice", "Anderson", "519-472-4910", "02", "19");
friendsList.addFriend(f1);
}
}
I tried all other methods defined in FriendsList.java but I get the same error message.
I understand that if the source files are in the same folder, the syntax to use a method from the other file is objectName.method(a).
What am I doing wrong?
(Sorry if I'm not asking it right, it's my first question)
I guess that you want to do the following instead:
public class MyFriends{
public void main(String[] args){
FriendsList friendsList = new FriendsList();
Person f1 = new Person("Alice", "Anderson", "519-472-4910", "02", "19");
friendsList.addFriend(f1);
}
}
You were instantiating an ArrayList<Person> but what you really want is to create an object of your own FriendsList class.
It seems that you don't have a no-args constructor in your FriendsList, so you need to do the following (instantiating a List of Person):
public class MyFriends{
public void main(String[] args){
FriendsList friendsList = new FriendsList(new ArrayList<Person>(100));
Person f1 = new Person("Alice", "Anderson", "519-472-4910", "02", "19");
friendsList.addFriend(f1);
}
}
Still, in my opinion, you should consider adding a no-args constructor to your FriendsList as follows so that my first suggestion would actually work (thanks @DavidConrad for the hints):
public class FriendsList{
ArrayList<Person> friendsList = new ArrayList<Person>(100);
// Constructor declaration of class
public FriendsList() {
}
public FriendsList(ArrayList<Person> friendsList){
this.friendsList.addAll(friendsList);
}
...
public void addFriend(Person friend){
friendsList.add(friend);
}
...
}
You are not actually using the FriendsList class. MyFriends should be:
public class MyFriends{
public void main(String[] args){
FriendsList friendsList = new FriendsList();
Person f1 = new Person("Alice", "Anderson", "519-472-4910", "02", "19");
friendsList.addFriend(f1);
}
}