Accessors, Mutators and Immutable Classes

• Accessor: does not change the state of the implicit parameter

double balance = account.getBalance();

• Mutator: modifies the object on which it is invoked

account.deposit(1000);

• Immutable class: has no mutator methods (e.g., String)

String name = "John Q. Public";
String uppercased = name.toUpperCase(); // name is not changed

• It is safe to give out references to objects of immutable classes; no code can modify the object at an unexpected time

Is the substring method of the String class an accessor or a mutator?

   Answer: It is an accessor – calling substring doesn't modify the string on which the method is invoked. In fact, all methods of the String class are accessors.

Is the Rectangle class immutable?

   Answer: No – translate is a mutator.