import java.io.File;

class WhilePractice {

  /**
   * @param theDogs a *non-empty* list, to find the average age of.
   */
  double averageAgeOf(  java.util.LinkedList<Dog>  theDogs  ) {
    double sumOfAges = 0.0;
  
    for (Dog d : theDogs) {
      sumOfAges = sumOfAges + d.getAge();
      }
      
     return (sumOfAges / theDogs.size());
  }  
    
  
  
  /** Return an oldest Dog in a list of Dogs.
   * @param theDogs The list of dogs to find the oldest of.
   *     Must be a non-empty list.
   * @return an oldest Dog in a list of Dogs.
   */
   Dog oldestDog( java.util.LinkedList<Dog> theDogs ) {
     
     Dog oldestSoFar = theDogs.get(0);
       
     for ( Dog d : theDogs ) {
       if (d.getAge() > oldestSoFar.getAge()) {
         oldestSoFar = d;
        }  
       }
     return oldestSoFar;
     }
    

     
  /** Return a list of *all* oldest Dogs, in a list of Dogs.
   * @param theDogs The list of dogs to find the oldest of.
   * @return a list of all the Dogs in the input which are tied for oldest-age.
   *     If the input list was empty, we return a (new) empty list.
   */
   java.util.LinkedList<Dog> oldestDogs( java.util.LinkedList<Dog> theDogs ) {
     java.util.LinkedList<Dog> retirementHome = new java.util.LinkedList<Dog>();
     
     if (theDogs.isEmpty()) {
       return retirementHome;  // If no dogs in input, then no dogs are oldest.
       }
       
       
     Dog anOldestDog = oldestDog( theDogs );
       
     for ( Dog d : theDogs ) {
       if (d.getAge() == anOldestDog.getAge()) {
         retirementHome.add( d );
         }  
        }
     return retirementHome;
     }
     
     
     
     
  /** Return The sum of the length of each file immediately inside directoryName.
   *    Doesn't recur into any sub-directories (but does include any size a directory
   *    itself takes up, aside from its sub-contents).
   * @param  directoryName  The pathname of a directory. 
   * @return The sum of the length of each file immediately inside directoryName.
   */
  public long directorySizeToplevel( String directoryName ) {
    // Convert the directoryName into a File object, so we can get its size etc.:
    File theDirectory = new File( directoryName );
    // Since we imported java.io.File above, we don't need to use its full name.
    
    if (theDirectory.isDirectory()) {

       long sizeSoFar = 0; // Accumulate the sum of all immediate file sizes.

       for ( File f : theDirectory.listFiles() ) {  // For each `f' in the directory,
         sizeSoFar = sizeSoFar + f.length();        // Add f's length to our sum.
         }

       return sizeSoFar;

       }
    else {
      // Hmm, this file wasn't a directory; print a message to System.err.
      String errMsg = "directorySizeTopLevel: " + directoryName + " is not the name of a directory.";
      System.err.println( errMsg );
      return -1;  // Is this an appropriate sentinel value?  I want to return 'false', but can't!
      }    
    }

  }