Creating mutable classes in Java 9

When we declare instance fields without the final keyword, we create a mutable instance field, which means that we can change their values for each new instance we create after the field is initialized. When we create an instance of a class that defines at least one mutable field, we create a mutable object, which is an object that can change its state after its initialization.

Note

A mutable object is also known as a mutating object.

For example, imagine that we have to develop a Web Service that renders elements in the 3D world and returns a high-resolution rendered scene. Such a task requires us to work with 3D vectors. First, we will work with a mutable 3D vector with three mutable fields: x, y, and z. The mutable 3D vector must provide the following features:

• Three mutable instance fields of type double: x, y, and z.

• A constructor that creates an instance by providing the initial values for the x, y, and z fields.

• A constructor that creates an instance with...