How to combine two array list and show in a listview in android

Combine two ArrayList into a single one

firstname1.addAll(first);

Please refer this article for sample code to concat two lists.

How to show these items in list view :

your layout should be ( as I used main.xml)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_marginTop="0dip"
android:background="@android:color/transparent">
    <ListView
            android:id="@+id/custom_list_view"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent"
            android:cacheColorHint="#00000000"
            android:fastScrollEnabled="true"
            android:background="@android:color/transparent"
            android:fadeScrollbars="true"
            android:layout_gravity="top"
            android:padding="2dp">
    </ListView>
</LinearLayout> 

and now Activity as CustomListView.java

public class CustomListView extends Activity {

    ArrayList<String> firstname1;
    ArrayList<String> first;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        firstname1 = new ArrayList<String>();
        first = new ArrayList<String>();
        //Let both array list having some data

        firstname1.add("firstname1_data1");
        firstname1.add("firstname1_data2");
        firstname1.add("firstname1_data3");
        firstname1.add("firstname1_data4");
        firstname1.add("firstname1_data5");
        firstname1.add("firstname1_data6");
        firstname1.add("firstname1_data7");
        firstname1.add("firstname1_data8");
        firstname1.add("firstname1_data9");
        firstname1.add("firstname1_data10");

        first.add("first_data1");
        first.add("first_data2");
        first.add("first_data3");
        first.add("first_data4");
        first.add("first_data5");
        first.add("first_data6");
        first.add("first_data7");
        first.add("first_data8");
        first.add("first_data9");
        first.add("first_data10");

        //Now copying value of first to firstname, as your requirement
        //Please refer http://www.java-examples.com/append-all-elements-other-collection-java-arraylist-example for sample code to concat two lists.
        firstname1.addAll(first);

        //Lets show your data into list view

        // Get a handle to the list view
        ListView lv = (ListView) findViewById(R.id.custom_list_view);

        lv.setAdapter(new ArrayAdapter<String>(CustomListView.this,
                android.R.layout.simple_list_item_1, firstname1));
        //Please refer http://developer.android.com/reference/android/widget/ListView.html for details of setAdapter()
    }
}

Happy coding.

List<String> a = new ArrayList<String>();
a.add("bla");
a.add("bla");
a.add("bla");
List<String> b = new ArrayList<String>();
b.add("Boo");
b.add("Boo");
b.add("Boo");

// Append content of a to b
b.addAll(a);

// New list containing a union b
List<String> union = new ArrayList<String>(a);
union.addAll(b);

To show that in a list view, you will need an adapter along with a list view. I recommend you read the Android Developer guide's tutorial about ListView: Hello ListView

public class HelloListView extends ListActivity {
  @Override
  public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    List<String> b = new ArrayList<String>();
    b.add("Boo");
    b.add("Boo");
    b.add("Boo");

    setListAdapter(new ArrayAdapter<String>(this,
            android.R.layout.simple_list_item_1, b));
  }
}