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Thread: Adding an array to an arraylist

  1. #1
    Junior Member
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    Default Adding an array to an arraylist

    Here is my code:

    public class NewMain{
        public static void main(String args[])
        {
             ArrayList<int[]> al=new ArrayList<int[]>();
            int a[]={1,2,3,4};
            al.add(a);
            a[0]=5;
            a[1]=6;
            a[2]=7;
            a[3]=8;
            al.add(a);
            for(int[] ar: al)
            {
                for(int k=0;k<a.length;k++)
                {
                System.out.print(ar[k]+" ");
                }
               System.out.println(); 
             }
     
     
     
        }
    }


    I get the output as

    5 6 7 8
    5 6 7 8

    Shouldn't it be
    1 2 3 4
    5 6 7 8

    What am I doing wrong?


  2. #2
    Super Moderator pbrockway2's Avatar
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    Default Re: Adding an array to an arraylist

    a is a reference to an array. You added that reference to the list twice so, when you print the list's contents, you get the values of that array printed twice.

    If you want the list to contain references to two different arrays you will need to create two different arrays. At the moment you say "int a[e]={1,2,3,4};" which creates one of the arrays. Later you have to say "a=new int[]{5,6,7,8}" to create the other one - or "a=new int[4]" and fill in its elements one at a time.

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