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Thread: newby Questions - indexOf help with an ArrayList

  1. #1
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    Default newby Questions - indexOf help with an ArrayList

    I'm trying to build an address book application, but before I start I'm familliaring my self with arrayLists of objects.

    I have two classes (and a third tester class):
    DirectoryEntry
    PhoneDirectory

    DirectoryEntry has a constructor that takes in two strings as arguments and saves then in class variables, name and number.

    (for now) all PhoneDirectory does is ceate an arraylist:

    dir = new ArrayList<DirectoryEntry>

    and has a method to add an entry to the array list.

    I want to us the indexOf("Stephen") to return an index number in the array, right now all I'm getting is -1.
    What bugs me is that if I put something like:

    DirectoryEntry name = dir.get(1);

    I get the name and number in slot 4. I'm just not understanding the indexOf() and OOP : S please any help would be most welcome


    public class Driver
    {
     
            public static void main(String[] args)
            {
                PhoneDirectory phone = new PhoneDirectory();
                phone.addEntry("Stephen", "447-8067");
                phone.addEntry("Vickie", "415-8006");
                phone.addEntry("Jake", "675-8064");
                phone.addEntry("Jen", "879-5684");
                phone.addEntry("Anna", "710-4564");
     
                phone.displayContents();
     
            }
     
     
     
    }

    import java.util.ArrayList;
     
     
    public class PhoneDirectory {
     
        public ArrayList<DirectoryEntry> dir;
     
        public PhoneDirectory()
        {
            dir = new ArrayList<DirectoryEntry>();
        }
     
        public void addEntry(String name, String number)
        {
            dir.add(new DirectoryEntry(name,number));
     
        }
     
        public void displayContents()
        {
     
           // DirectoryEntry aName = dir.get(3);
            int ind = dir.indexOf("Stephen");
     
            System.out.println(ind);
        }
    }

    public class DirectoryEntry {
        private String name;
        private String number;
     
        public DirectoryEntry(String name, String number)
        {
            this.name = name;
            this.number = number;
        }
     
        public String name()
        {
            return name;
        }
     
    @Override
         public String toString()
        {
            return name + " " + number;
        }
    }


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: newby Questions - indexOf help with an ArrayList

    I want to us the indexOf("Stephen") to return an index number in the array,
    Is the String "Stephen" an object in the ArrayList?
    Or is it inside of another object, a DirectoryEntry?
    It looks like the ArrayList contains DirectoryEntry objects, not Strings.

  3. #3
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    Default Re: newby Questions - indexOf help with an ArrayList

    What Norm said.
    Also:
    DirectoryEntry name = dir.get(1); I get the name and number in slot 4
    Call my cynical, but I absolutely doubt that It's returning the 4th ArrayList entry based on the code you posted.

    Edit: To add to Norms post, check out indexOf and read the notes under 'returns'.
    Last edited by newbie; September 20th, 2011 at 06:48 PM.
    Please use [highlight=Java]//code goes here...[/highlight] tags when posting your code

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    Default Re: newby Questions - indexOf help with an ArrayList

    I won't call you cynical but I will call you cautious...Sorry, the actual code was:
    do
    DirectoryEntry aName = dir.get(3); < - This actually does work, as you can see I'm using get on a DirectoryEntry object - I just don't know how to do something like this to search and get an index number. if I do this:

    DirectoryEntry aName = dir.indexOf("Stephen"); I get bupkis

  5. #5
    Super Moderator Norm's Avatar
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    Default Re: newby Questions - indexOf help with an ArrayList

    DirectoryEntry aName = dir.indexOf("Stephen"); I get bupkis
    To find the element in the list with that contents you will need a loop that looks at each element in the list and tests if it contains the contents you want.

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    Default Re: newby Questions - indexOf help with an ArrayList

    DirectoryEntry aName = dir.get(3);
    The first index in an ArrayList starts at 0.
    So when you say get(3), you're actually referring to the 4th entry.
    Please use [highlight=Java]//code goes here...[/highlight] tags when posting your code

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