Message passing

• Objects communicate by sending messages.
• Messages convey some form of information.
• An object requests another object to carry out an activity by sending it a message.
• Most messages pass arguments back and forth.
• Meilir Page-Jones defines three types of messages[12]:
  1. Informative - send information for the object to update itself.
  2. Interrogative - ask an object to reveal some information about itself
  3. Imperative - take some action on itself, or another object
• Grady Booch defines four types of messages[4]:
  1. Synchronous - receiving object starts only when it receives a message from a sender, and it is ready.
  2. Balking - sending object gives up on the message if the receiving object is not ready to accept it.
  3. Timeout - sending object waits only for a certain time period for the receiving object to be ready to accept the message.
  4. Asynchronous - sender can send a message to a receiver regardless of whether the receiver is ready to receive it.