In this tutorial we will see how to copy and add all the elements of a list to ArrayList. In order to do that we will be using addAll method of ArrayList class.
public boolean addAll(Collection c)
It adds all the elements of specified Collection c to the end of the calling list. It throws NullPointerException if the specified Collection is null.
Complete Example of Copying List elements to ArrayList
package beginnersbook.com;
import java.util.ArrayList;
import java.util.List;
public class ListToArrayListExample {
public static void main(String a[]){
ArrayList<String> al = new ArrayList<String>();
//Adding elements to the ArrayList
al.add("Text 1");
al.add("Text 2");
al.add("Text 3");
System.out.println("ArrayList Elements are: "+al);
//Adding elements to a List
List<String> list = new ArrayList<String>();
list.add("Text 4");
list.add("Text 5");
list.add("Text 6");
//Adding all lements of list to ArrayList using addAll
al.addAll(list);
System.out.println("Updated ArrayList Elements: "+al);
}
}
Output:
ArrayList Elements are: [Text 1, Text 2, Text 3] Updated ArrayList Elements: [Text 1, Text 2, Text 3, Text 4, Text 5, Text 6]
addAll() method is not throwing nullpointerException.if the list is empty
@ Himanshu,
ArrayList never be a null, instead it is an empty when u create. if you want more clarity, execute the below code.
List list = new ArrayList();
List newList = new ArrayList();
list.addAll(newList);
System.out.println(list); // this works fine and creates a list with empty
List list = null;
List newList = null;
list.addAll(newList);
System.out.println(list); // this will give you NPE. since List is not initiated with any of its implemented class