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Thread: ArrayList Problem

  1. #1
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    Default ArrayList Problem

    Alright so far i've created the list, and am able to add/delete certain things from the list when neccessary.

    Heres what I have..

    public static ArrayList<String> cSP = new ArrayList<String>();
    cSP.add(c.playerName);


    Now my problem is, I need to be able to pull a random String from inside the ArrayList, i've searched around but can't find out how.

    Thanks,
    Marty


  2. #2
    Member Truffy's Avatar
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    Default Re: ArrayList Problem

    Hi Marty,

    Welcome to the java programming forums.

    Can you pls give all your codes so we can figure it out.

    Thanks.

    Cheers,
    Truffy

  3. #3
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    Default Re: ArrayList Problem

    Quote Originally Posted by Truffy View Post
    Hi Marty,

    Welcome to the java programming forums.

    Can you pls give all your codes so we can figure it out.

    Thanks.

    Cheers,
    Truffy
    Thats basically all i have..

    It adds it to the list fine as i had it print the list and it showed the playerName after it was added, just i need to add a method that picks a random String from inside of the list.

  4. #4
    Member Truffy's Avatar
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    Default Re: ArrayList Problem

    Quote Originally Posted by Marty View Post
    Thats basically all i have..

    It adds it to the list fine as i had it print the list and it showed the playerName after it was added, just i need to add a method that picks a random String from inside of the list.
    heres a sample code that might help.

    import java.util.ArrayList;
     
    public class Main {
      public static void main(String[] args) {
        ArrayList<String> arrayList = new ArrayList<String>();
        arrayList.add("1");
        arrayList.add("2");
        arrayList.add("3");
     
        arrayList.add(1, "INSERTED");
        for (String str: arrayList)
          System.out.println(str);
      }
    }

    output:
    /*
    1
    INSERTED
    2
    3
    */

    hope it helps because in that you ca add a method to randomlu pull the list youd added.

    Cheers,
    Truffy

  5. #5
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    Default Re: ArrayList Problem

    Quote Originally Posted by Truffy View Post
    heres a sample code that might help.

    import java.util.ArrayList;
     
    public class Main {
      public static void main(String[] args) {
        ArrayList<String> arrayList = new ArrayList<String>();
        arrayList.add("1");
        arrayList.add("2");
        arrayList.add("3");
     
        arrayList.add(1, "INSERTED");
        for (String str: arrayList)
          System.out.println(str);
      }
    }

    output:
    /*
    1
    INSERTED
    2
    3
    */

    hope it helps because in that you ca add a method to randomlu pull the list youd added.

    Cheers,
    Truffy
    I don't want to pull the list, I want to pull a random string from the list.

  6. #6
    Member Truffy's Avatar
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    Default Re: ArrayList Problem

    can u explain fartehr what you want to try. im sorry got lost.

  7. #7
    mmm.. coffee JavaPF's Avatar
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    Default Re: ArrayList Problem

    Hello Marty,

    Welcome to the Java Programming Forums

    I believe this is what you are looking for:

    import java.util.ArrayList;
    import java.util.Random;
     
    public class Marty {
     
        /**
         * JavaProgrammingForums.com
         */
        public static void main(String[] args) {
     
            ArrayList<String> arrayList = new ArrayList<String>();
            arrayList.add(0, "Java");
            arrayList.add(1, "Programming");
            arrayList.add(2, "Forums");
            arrayList.add(3, ".com");
     
            // Generate random number 0 - 3
            Random random = new Random();
            int rand = random.nextInt(4);
     
            // Convert ArrayList to Object array
            Object[] elements = arrayList.toArray();
     
            // Print array element at random number
            System.out.println(elements[rand]);
        }
    }
    Please use [highlight=Java] code [/highlight] tags when posting your code.
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  8. #8
    Member Truffy's Avatar
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    Default Re: ArrayList Problem

    Quote Originally Posted by JavaPF View Post
    Hello Marty,

    Welcome to the Java Programming Forums

    I believe this is what you are looking for:

    import java.util.ArrayList;
    import java.util.Random;
     
    public class Marty {
     
        /**
         * JavaProgrammingForums.com
         */
        public static void main(String[] args) {
     
            ArrayList<String> arrayList = new ArrayList<String>();
            arrayList.add(0, "Java");
            arrayList.add(1, "Programming");
            arrayList.add(2, "Forums");
            arrayList.add(3, ".com");
     
            // Generate random number 0 - 3
            Random random = new Random();
            int rand = random.nextInt(4);
     
            // Convert ArrayList to Object array
            Object[] elements = arrayList.toArray();
     
            // Print array element at random number
            System.out.println(elements[rand]);
        }
    }
    great post Sir. Shame i didn't understand what he meant. Anyway, thanks.

  9. #9
    mmm.. coffee JavaPF's Avatar
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    Default Re: ArrayList Problem

    Thanks Truffy. Thank you for your efforts too
    Please use [highlight=Java] code [/highlight] tags when posting your code.
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  10. #10
    Member Truffy's Avatar
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    Default Re: ArrayList Problem

    Quote Originally Posted by JavaPF View Post
    Thanks Truffy. Thank you for your efforts too
    Your welcome.

    Cheers,
    Truffy

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    Default Re: ArrayList Problem

    The only thing I would add to this is to put the random generator into a function/method so that you can continually recall the random function.You could even put the whole thing into a while loop so that while a certain condition is true it continually pulls random positions from the ArrayList. I would even seed the random function using the system time. Happy Programming.

  12. #12
    Member Darryl.Burke's Avatar
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    Default Re: ArrayList Problem

    Spam reported

    db

  13. #13
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    Default Re: ArrayList Problem

    Sorted, thanks Darryl.Burke

    // Json

  14. #14
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    Default Re: ArrayList Problem

    I would do it a little differently.

    import java.util.ArrayList;
    import java.lang.Math;
     
    public class Marty {
     
        /**
         * JavaProgrammingForums.com
         */
        public static void main(String[] args) {
     
            ArrayList<String> arrayList = new ArrayList<String>();
            arrayList.add(0, "Java");
            arrayList.add(1, "Programming");
            arrayList.add(2, "Forums");
            arrayList.add(3, ".com");
     
            // Generate random number 0 - 3
            int rand = (int)(Math.random()*4);
     
            // Print array element at random number
            System.out.println(arrayList.get(rand));
        }
    }

    I'll explain what I did:

     int rand = (int)(Math.random()*4);
    This will return a random number between 0 and 3. The Math.random() method returns a random double greater than or equal to 0 and less than 1. So, if we multiply the result by 4, it will give us a random number greater than or equal to 0 and less than 4. BUT, we also have to cast it as an int because the ArrayList.get(int n) method doesnt accept a double. So to convert a double to an int, we simply say (int)(double number) and that turns our double to an int by cutting off the decimal.

    System.out.println(arrayList.get(rand));
    This will use the ArrayList's predefined method to get an element of the arraylist based on the index number. This way we dont have to move our elements into an array.

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    Default Re: ArrayList Problem

    try:

    int rand=(int)(Math.random()*ArrayListName.size());
    System.out.println(ArrayListName.get(rand));

  16. #16
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    Default Re: ArrayList Problem

    Quote Originally Posted by cosecant View Post
    try:

    int rand=(int)(Math.random()*ArrayListName.size());
    System.out.println(ArrayListName.get(rand));
    Ya, I thought about that afterwards. That is a better one because ArrayListName.size() will change the range of the random numbers when you add more items to the array.

  17. #17
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    Default Re: ArrayList Problem

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