The Importance of Encapsulation

• Even a simple class can benefit from different implementations
• Users are unaware of implementation
• Public instance variables would have blocked improvement
  • Can't just use text editor to replace all
    

    d.year
    

    with
    

    d.getYear()
    

  • How about
    

    d.year++?
    

  • d = new Day(d.getDay(), d.getMonth(), d.getYear() + 1)
    

  • Ugh--that gets really inefficient in Julian representation
• Don't use public fields, even for "simple" classes
• Private data members facilitate changes to implementation without disrupting users