Implementing Domain-Driven Design

Value Equality

When a Value Object instance is compared to another instance, a test of object equality is employed. Throughout the system there may be many, many Value instances that are equal, and yet not the same objects. Equality is determined by comparing the types of both objects and then their attributes. If both the types and their attributes are equal, the Values are considered equal. Further, if any two or more Value instances are equal, you could assign (using replacement) any one of the equal Value instances to an Entity’s property of that type and the assignment would not change the value of the property.

Here’s an example of class FullName implementing a test for Value equality:

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public boolean equals(Object ...