This is not an Array, but a List
(albeit an ArrayList being backed by an array internally, but that’s implementation detail and slightly beside the point here).
When you add a Student to your list, it becomes an element of that list.
You can access List
elements using list.get(int index)
.
“Mark” or 23 in your example are not elements of the list, but properties of the Object “Student” (remember that in Java, class names are CamelCase and usually singular by convention)
Therefore, what I think you want is something like:
Student mark = new Student("Mark", "Markos", 23, 32);
//assuming a constructor exists e.g.:
//Student(String firstname, String lastname, int age, int studentNumber)
here.add(mark);
Student stillMark = here.get(0); //assuming no other modification
String marksName = mark.getName(); //"Mark", assuming this getter exists
int marksAge = mark.getAge(); //23, ditto
mark.setAge(24); //who's birthday is it?
System.out.println(stillMark.getAge()); //24 - mark and stillMark point to exactly the same object.
These are basic Java (and other programming language) concepts. Good luck with your learning.
Edit: Calculate the average age on Java 8+ (also see Calculating average of an array list?)
OptionalDouble avgAge = list
.stream() //Use Java 8 streams to iterate
.mapToInt(Student::age) //transform into an IntStream
.average(); //IntStream has this beautiful method
if(avgAge.isPresent()) {
//this will be false if the list was empty.
}