org.seedstack.business.domain.ValueObject Maven / Gradle / Ivy
/*
* Copyright © 2013-2024, The SeedStack authors
*
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/.
*/
package org.seedstack.business.domain;
/**
* A value object measures, quantifies or describes something in the domain. A value object has no
* lifecycle from the domain perspective. As such we don’t need to provide him an identity. Value
* objects can be created and destroyed at will without any impact.
*
* A value object is immutable, meaning that its state cannot be changed after creation. If you
* need to change a value object, create a new one derived from the initial one. Value object
* immutability means that they can be easily shared across the whole system.
*
* A value object describes a conceptual whole. All of its attributes are related to each other
* and are all participating to the description of the thing.
*
* As entities, value objects should contain behavior that is relevant to them. If the domain
* concept described by the value object has a behavior, write methods encapsulating it. This
* behavior must remain side-effect free (not depending upon any mutable state).
*
* The {@code BaseValueObject} class can be used as a base class for domain entities. It already
* implements the {@link #equals(Object)} and {@link #hashCode()} methods properly.
*
* Example:
*
* public class SomeValueObject implements ValueObject {
* private String attribute1;
* private String attribute2;
*
* public SomeValueObject(String attribute1, String attribute2) {
* this.attribute1 = attribute1;
* this.attribute2 = attribute2;
* }
*
* {@literal @}Override
* public int hashCode() {
* // implement based on all attributes
* }
*
* {@literal @}Override
* public boolean equals() {
* // implement based on all attributes
* }
*
* // Other methods
* }
*
*/
@DomainValueObject
public interface ValueObject extends Producible {
/**
* As per Domain-Driven Design semantics, value object equality must be computed on all its
* attributes.
*
* @param other other object.
* @return true if the other object is of the same class as this value object and if all
* attributes are equals, false otherwise.
*/
boolean equals(Object other);
/**
* As per Domain-Driven Design semantics, the hash code of a value object must be computed on all
* its attributes.
*
* @return a hash code value for this value object.
*/
int hashCode();
}