store data array list

ArrayList a1 = new ArrayList();
a1.Add( "1" );
ArrayList a2 = new ArrayList();
a2.Add( "2" );
ArrayList a3 = new ArrayList();
a3 = a2; //or a3 = a1; where-ever you want to copy data from.

Hi,

Build arrays A & B, add values in array C[^] this will be helpful to you.

clone() method and manual way of adding two ArrayList is already mentioned above.
Here is the another way of merging two ArrayList into 3rd ArrayList. There is a method addAll which can be used for adding all the elements of a list to another list.

Lets say list is of String type. This is the way you should do it:

ArrayList<string> al1= new ArrayList<string>();
al1.add("1");
al1.add("2");
al1.add("3");
ArrayList<string> al2= new ArrayList<string>();
al2.add("1st");
al2.add("2nd");
al2.add("3rd");

//Final ArrayList
ArrayList<string> al3= new ArrayList<string>();
//Adding elements of arraylist1 to arraylist3
al3.addAll(al1);
//Adding elements of arraylist2 to arraylist3
al3.addAll(al2);

Source:
http://beginnersbook.com/2013/12/how-to-joincombine-two-arraylists-in-java/[^]

http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#addAll(java.util.Collection)[^]

You can do it with Linq:

List<string> list1 = new List<string>();
list1.Add("HHello");
list1.Add("Hello");
list1.Add("HelloO");
List<string> list2 = new List<string>();
list2.Add("HHello");
list2.Add("HelloX");
list2.Add("HelloO");
var list3 = from s in list1
        join t in list2
                    on s equals t
                    select s;
foreach (var v in list3)
        {
    Console.WriteLine(v);
        }

It might be helpful,

class Program
{
    static void Main(string[] args)
    {

        List<string> listOne = new List<string>() { "listTwo_1", "listTwo_1", "listOne_3", "listTwo_1" };
        List<string> listTwo = new List<string>() { "listTwo_1", "listTwo_2", "listTwo_3", "listTwo_1" };
        Common(listOne, listTwo).ForEach(item => Console.WriteLine(item));
    }

    static List<string> Common(List<string> first, List<string> second)
    {
        return first.Where(item => second.Contains(item)).Distinct().ToList<string>();
    }
}

:)