Kas peaks arvesse võtma andmeklassi equals meetodi üle kirjutamisel põhiklassi välju?

In Kotlin, a data class automatically generates the equals, hashCode, and toString methods, considering only the properties declared within the class itself. If your class inherits from a base class with its own fields, these fields are not included in the comparison by default.

If the comparison logic needs to consider the base class's fields, it is recommended to override the equals method manually, calling super.equals(other) and adding checks for the base class's fields. Otherwise, if the base class does not contain relevant data for comparison, you can rely on the generated method.

Example of overriding equals considering the base class:

open class Base(val id: Int) {
    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other !is Base) return false
        return id == other.id
    }

    override fun hashCode() = id
}

data class Derived(val name: String) : Base(0) {
    override fun equals(other: Any?): Boolean {
        if (this === other) return true
        if (other !is Derived) return false
        if (!super.equals(other)) return false
        return name == other.name
    }

    override fun hashCode() = super.hashCode() * 31 + name.hashCode()
}

Therefore, if the base class's fields are important for object comparison, they should be included in the equals method.