Access to Objects

Access to objects is accomplished by sending messages to them.

• Retrieving data values:
  (send obj x) or obj.getX()
  
  If x is a private data field, getX() is called an accessor or getter method.

• Setting data values:
  (send obj x: 3) or obj.setX(3)
  
  If x is a private data field, setX() is called a mutator or setter method.

• Requesting actions:
  (send obj print) or obj.print()

A message or method call is like a function call, but which function is called depends on the runtime type (class) of the object.

Wrapping access to a field in accessor methods helps information hiding, but hurts efficiency.