This is information you can google... it's a list that can expand or contract but takes up more memory since it needs to take objects rather than primitive data types.
Well it's a data structure that groups together a bunch of a specific type of Objects (no primitives). This is organized in a list like format and does not have a set size unlike arrays. It's very simple to use. Here's the javadoc for it: https://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html
That lists how to construct it, all of the various methods it contains, basically anything you might need to know
Wait, if an assignment requires you to use this specific structure, your lecturer shouldh've already gone through it in class. Why don't you try going through your course lecture notes?
I like to think of data types as boxes, and array lists are like a chain of boxes connected together. One box can hold one thing big or small but a chain of boxes can hold things of various sizes, though of only one type of thing. You can't keep numbers(int,double etc.) with letters and sentences (char, string etc.). One important thing to keep in mind and continually remember is that when it comes to things like lists is that the index or box location number usually is 0. So if you have an array of size 3 the boxes would be array[0] array[1] and array[2], there is no array three because 2 is three.
Array...just think about it as a collection of things. Well, at first its difficult but as you get used to it, it will become easy. For simple example: int [] wonka = new int[3]; This is compose of data type (int or integer) and the bracket[] which indicates that its an array. I assume that you know diferent data types liek char, int, float and so on. This one new int[3]; means that it's instantiated and the number 3, is the size of array. And remember, always remember, array starts at zero. Yes its zero. Whenever you access or try to put something in the array, you always begin at zero even though its size is 3. Weird right? but you will get used to it. Hehe For quick example: wonka[3]=[1, 2, 3]; // here is the one line example of adding values to the array or you can do this manually. wonka[0] = 1; wonka[1] = 2; wonka[2] = 3; You notice that in wonka[0] = 1; It starts with zero and its value is 1 (you can manipulate its value if you want) And it ends at wonka[2] right? yup that's its array number..even though we select its size as 3, its array number will always end with minus one (-1). Remember that the array number will always (-1) to the specified length (we select 3 before) because it starts at array number zero. Please reread this if you dont understand and try to access w3schools, youtube videos and your book because it will be helpful to you. In getting the values you can do this System.out.print("first wonka number is" + wonka[0]); Output is: first wonka number is 1 Looping will be soon used in array as they will always partners in crime as you go forward in your study so study loops in advance.But focus first in array. Be warned that complex array will be on your way. Happy JAVA!!!hahahaha
why don't you post the picture then or go onto tutorialspoint, just google arraylist and they tell you all about them