3
class PersonDemo // Fig 4.9, pg 103
{
    public static void printAll( Person[ ] arr )
    {
        for( int i = 0; i < arr.length; i++ )
        {
            if( arr[ i ] != null )
            {
                System.out.print( "[" + i + "] " + arr[ i ] );
                System.out.println( );
            }
        }
    }
   
    public static void main( String [ ] args )
    {
        Person [ ] p = new Person[ 4 ];
        p[0] = new Person( "joe", 25, "New York", "212-555-1212" );
        p[1] = new Student( "becky", 27, "Chicago", "312-555-1212", 4.0 );
        p[3] = new Employee( "bob", 29, "Boston", "617-555-1212", 100000.0 );
       
        if( p[3] instanceof Employee )
            ((Employee) p[3]).raise( .04 );
      
        printAll( p );
    }
}