UserBuilder.kt

class UserBuilder() {

    var firstName: String? = null
    var middleName: String? = null // optional
    var lastName: String? = null
    var address: Address? = null
    var contact: Contact? = null // optional
    var company: Company? = null // optional
    var educations: List<Education>? = null

    fun setFirstName(firstName: String) {
        this.firstName = firstName
    }

    fun setMiddleName(middleName: String) {
        this.middleName = middleName
    }

    fun setLastName(lastName: String) {
        this.lastName = lastName
    }

    fun setAddress(address: Address) {
        this.address = address
    }

    fun setContact(contact: Contact) {
        this.contact = contact
    }

    fun setCompany(company: Company) {
        this.company = company
    }

    fun setEducations(educations: List<Education>) {
        this.educations = educations
    }

    fun build(): User {
        return User(
            firstName!!,
            middleName,
            lastName!!,
            address!!,
            contact,
            company,
            educations!!
        )
    }
}