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Law of Demeter

• The law: A method should only use objects that are
• • instance fields of its class
  • parameters
  • objects that it constructs with new
• Shouldn't use an object that is returned from a method call
• Remedy in mail system: Delegate mailbox methods to mail system
  mailSystem.getCurrentMessage(int mailboxNumber);
  mailSystem.addMessage(int mailboxNumber, Message msg);
  . . .
• Rule of thumb, not a mathematical law

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