Planned lessonMID-060-L03

Entities and value objects

Lesson 3 of 7
Mid-level

On This Lesson 4 topics

In this lesson
Planned topics
Draft outline details
Practice

This lesson is planned. The outline below lists the topics it will cover. The full lesson has not been published yet.

In this lesson

model identity versus value in Java.

Planned topics

An entity has an identity that persists as its attributes change: Order with OrderId.
A value object has no identity; equal values are interchangeable: Money, Address. It is immutable.
Java records fit value objects well and validate in the compact constructor.
Entity equality is by ID; value equality is by all fields.
Prefer value objects over primitives (Money instead of BigDecimal plus a currency string).

Draft outline details

Demonstration

java

public record Money(BigDecimal amount, Currency currency) {
    public Money {
        if (amount.signum() < 0) throw new IllegalArgumentException("negative");
    }
    public Money plus(Money o) { /* same currency check */ return new Money(amount.add(o.amount), currency); }
}

Check your understanding

Which one is Money, entity or value object?

Show answer

Value object.

Practice

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