Java Video Tutorial, Web Design

Java Video Tutorial 11

35 Comments

Java Video Tutorial 11In this part of my Java Video Tutorial I introduce Java collection classes. Specifically I cover how to use Java ArrayLists.

Java ArrayLists make it easy to keep track of groups of objects. A Java ArrayList differs from a java array in that it automatically resizes itself when you add or remove values.

I’ll go over nearly every Java ArrayList method in the video below. The code follows the video and it is heavily commented to help you learn easily.

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Code From the Video

35 thoughts on “Java Video Tutorial 11”

  1. HELLO AGAIN DEREK I WROTE TO YOU AND ASKED YOU THIS QUESTION BEFORE BUT I GUESS YOU’RE A BUSY MAN. I FOLLOWED THIS VIDEO TUTORIAL ON THE COLLECTIONS. YOU IMPORTED SEVERAL CLASS LIKE ITERATORS AND SUCH. CAN YOU IN THAT SITUATION JUST IMPORT JAVA.UTIL* FOR ALL THE CLASSES NECESSARY TO GET THE JOB DONE? THANKS

    Reply

    1. At the very least I think this would dramatically slow down your program. I’m going to check, but I’d advise against doing that. I must have missed one of your messages. Sorry about that

      Reply

  3. Hey Derek i am a keen follower of your website,i just want to say that these tutorials are awesome and i hope u will put some programming tutorials on c++.God bless you.

    Reply

  6. How many ArrayLists can you create in one file? If you can create more than one, then how do you specify which arraylist you are adding elements to? names.add() seems very general.

    Thanks.

    Reply

  7. Derek – you do a GREAT job with these lessons. Could you recommend a good text that might supplement your tutorials? Preferably a book with follow up exercises. thanks

    Reply

    1. Thank you very much 🙂 Everyone I talk to recommends the Head First Java book. I can’t think of a book that gets more good reviews. Stay away from technical books like Thinking in Java and you’ll be fine.

      Reply

  8. Object[] moreNames = new Object[4];
    moreNames = nameCopy.toArray();
    System.out.println(Arrays.toString(moreNames));

    Hey Derek,
    Tell me why do we need Object array to copy the arraylist into.

    I am getting the same thing by doing this.

    System.out.println(Arrays.toString(nameCopy.toArray()));

    any specific reason doing that way and also not giving the object array size doesnt make any difference.Even after putting 1 in the arraysize,the output is showing all the nameCopy list items.
    I dont understand what is going on at the backside.

    Reply

  9. – Hi Derek –

    – Thank You for the tutorials – much obliged – !

    – Would You help me with ArrayLists further… – (?)

    – I have a scenario where I have a Vehicle Class with Vehicle Objects contained in an ArrayList – I have another Class, ‘Showroom’ to hold a Vehicle Objects ArrayList (The Showroom Constructor initialises the Vehicle Objects ArrayList) – I have managed to do this –

    – The Vehicles have an attribute (String) that contains their Registration / ID Number – I am able to search for a Vehicle Object, by passing the Registration Number attribute into a ‘findVehicle’ method in the Showroom Class –

    – I have to set a ‘currentVehicle’, again by passing in the Reg. No. attribute – I have managed to do this also –

    – the problem I am having though, is accessing / returning the next & previous Vehicle in the ArrayList –

    – I am wanting to have both a ‘nextVehicle’ & a ‘previousVehicle’ method that moves forward & backwards though the ArrayList from a start-point of the ‘currentVehicle’ –

    – When the ‘nextVehicle’ is returned, it is supposed to then become the ‘currentVehicle’ – likewise with the ‘previousVehicle’ method –

    – How might I iterate forwards & backwards through the ArrayList & return the appropriate Vehicle Object – (?)

    – I hope I have been clear… – I’m quite new to Java –

    – Any help is much appreciated –

    – Thanks –

    D.

    Reply

    1. – I need to clarify… – that the Vehicle Class has the Vehicle Attributes (e.g. Reg No. / Make / Model etc.), & the ArrayList of Vehicles is initialised by the Showroom Class –

      – Sorry if I’m not being clear –

      D.

      Reply

    1. To generate a random number using math.random you could do this to generate a number between 1 and 10 : int n = (int)(10.0 * Math.random()) + 1;

      This translates into int n = (int)(LargestNumber * Math.random()) + Smallest Number;

      Math.random() returns numbers between 0.0 to 0.999

      You could also use
      Random rand = new Random();
      int value = rand.nextInt(10);

      This gives you a number between 0 and 9. rand.nextInt(10) + 1; would give you numbers between 1 and 10.

      I hope that helps 🙂

      Reply

  12. Hey Derek. I’m pretty new to Java, have only been programming for 3 days. My question is, at the moment my ArrayList only accepts Strings as I have set it to accept only Strings, How do I make my ArrayList accept both doubles Strings. code is as follows:

    //Name of class
    public class Profile{

    //Variables

    String Carbchoice = “rice”;
    double Height = 155.0;

    ArrayList arrayListOne = new ArrayList();

    ArrayList UserProfile = new ArrayList();

    //Method
    public void AddingToList(){

    UserProfile.add(CarbChoice);
    UserProfile.add(Height); //this is what I would like to do

    }
    }

    Reply

    1. You could use something like this ListyourList = new ArrayList (); or you could create a custom object that can contain doubles, or strings and use something like this List yourList = new ArrayList ();

      Reply

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