Java Illuminated, 5th Edition

7.6 Writing Mutator Methods

As we have discussed, we declare the instance variables as private to encapsulate the data of the class. We allow only the class methods to directly set the values of the instance variables. Thus, it is customary to provide a public mutator method for any instance variable that the client will be able to change. Because the method names usually start with “set,” mutator methods are often called setters.

The general form of a mutator method is the following:

public void setInstanceVariable( dataType newValue )
{
    // validate newValue, then assign to the instance variable
}

SOFTWARE ENGINEERING TIP

Provide a mutator method for any instance variable that you want to allow the client to change.

We declare mutator ...