You need to use the new operator when creating the object
Contacts.add(new Data(name, address, contact)); // Creating a new object and adding it to list - single step
or else
Data objt = new Data(name, address, contact); // Creating a new object
Contacts.add(objt); // Adding it to the list
and your constructor shouldn’t contain void. Else it becomes a method in your class.
public Data(String n, String a, String c) { // Constructor has the same name as th