how to change elements of arrayList in java

/**
 * @author lautturi.com
 * Java example: java modify element in an array list
 */
import java.util.*;

public class Lautturi {

	public static void main(String[] args) {

		ArrayList<String> arrList = new ArrayList<String>();
		arrList.add("lautturi");
		arrList.add("java");
		arrList.add("python");
		arrList.add("hello");
		
	    System.out.println("ArrayList: " + arrList);
	    arrList.set(3, "js");
	    System.out.println("Modified ArrayList: " + arrList);
	}
}

output:

ArrayList: [lautturi, java, python, hello]
Modified ArrayList: [lautturi, java, python, js]