Listing A

import java.io.IOException;
  import java.util.LinkedList;
  import java.util.List; import java.util.Iterator;
public class Scheduler {

       private List todoList = new LinkedList();
       
       public long getTotalDuration() throws Exception {
                     long total = 0L;
                       for (Iterator i=todoList.iterator(); i.hasNext();  ) {
                                    total += ((Task)(i.next())).getDuration();        
                       }        
                       return total;    
       }    
       public void main(String[] args) {
                      Scheduler s = new Scheduler();        
                      s.todoList.add(new DownloadTask("http://google.com"));        
                      try {
                                  System.out.println(s.getTotalDuration());        
                      } catch (Exception doh) {
                                  doh.printStackTrace();        
                      }   
        }
 } 
 interface Task {
        long getDuration() throws Exception;} 
 class DownloadTask implements Task {
        private String url;    
        public DownloadTask(String u) {
                      url = u;    
        }
              
        public long getDuration() throws IOException {
                       // this may throw an IOException    
        }
  }