Java ArrayList

public class ArrayListDemo {

 public static void main(String[] args) {
  /**
   * Following example will cause a run time exception:
   * java.lang.ClassCastException, although no compilation error happened.
   */
  
  /*
   * int sum = 0; 
   * ArrayList al = new ArrayList(); 
   * al.add("1"); 
   * al.add(new Integer(2));
   *  for (int i = 0; i < al.size(); i++) { 
   *  sum+= (Integer)al.get(i); 
   *  } 
   *  System.out.println(sum);
   */

  /**
   * Following example will fix above problem.
   */
  int sum = 0;
  ArrayList al = new ArrayList();
  // al.add("1"); this line has a compilation error.
  al.add(new Integer(1));
  al.add(new Integer(2));
  for (int i = 0; i < al.size(); i++) {
   sum += (Integer) al.get(i);
  }
  System.out.println(sum);
 }

}