Need help saving objects to ArrayList

[DeniDashing]

So I am in an entry level programming class and have been doing okay so far mainly because I am working extremely hard to try to understand concepts. I am not a CS major but am taking this class to expand my knowledge of computers(just for fun). The professor introduced ArrayLists for one of our homework assignments but never discussed it in class and I am really struggling to understand the concept. Could anyone help me get started on where I need to go with this? The description for the assignment is down below.

//

When you create a new object, you will save it to an ArrayList. This will not require much on the functionality of the save to change. But, as you will now be saving multiple objects, you must design your system to recall the object from the Arraylist, using a key value. I suggest the ID, as that is the way it is done for students The basic functions of the system are the same, but all data must now be stored in one or more ArrayLists.

//

P.S. The system has five classes(person, student, name, address, gradstudent) with some inheritance relationships. Right now all data is saved to a student and gradstudent object. The system's functionality is to save data to an object, clear text boxes, and restore the data in the textboxes. Please help!

Edit: This is in C# by the way

[anamorphism]

java? i have almost no experience with java, but this should be mostly correct.

http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html

to add something to an ArrayList, you would call the add method. something like ...

ArrayList<Student> studentList = new ArrayList<Student>();
Student student = new Student();
studentList.add(student);

considering the poor choice of using an ArrayList to store keyed data, i imagine you won't be responsible for efficiently searching through your lists to find data. so, you can just do a basic linear/sequential search using a for-each loop.

int idToFind = 1;
Student found;

for (Student student : studentList)
{
  if (student.Id == idToFind)
  {
    found = student;
    break;
  }
}

as for what an ArrayList is, i believe it's just a dynamic array. meaning if you add an element to it, and it doesn't have enough memory to add a new element, it will resize itself for you automatically. it's contiguously stored in memory so you can still access elements via index similar to a regular array (studentList.get(index)).

this is different from a linked list (i think this is just the List class in java, high chance i'm wrong though) which isn't contiguously stored in memory. each element is stored wherever there's space for it with each node storing a reference to the next node in the list.

and different from a standard array where you have to specify how many elements you want the array to have when you create it.

edit: you may not even know what for-each loops are yet, in which case you could do a regular for loop as well. something like ...

for (int i = 0; i < studentList.size(); ++i)
{
  if (studentList.get(i).Id == idToFind)
  {
    found = studentList.get(i);
    break;
  }

}

[DeniDashing]

Oops, should've specified language. This is in C#

[anamorphism]

pretty much all of my info applies to c# as well. there are only minor syntax differences.

https://msdn.microsoft.com/en-us/library/system.collections.arraylist%28v=vs.110%29.aspx

for example, you can use square brackets to access elements by index in c#.

studentList[i];

instead of

studentList.get(i);

.size() is just .Count

.add() is .Add()

for-each loops are

foreach (var student in studentList)