Design Pattern

 * Builder

class User private constructor(
	firstName: String?,
	middleName: String?, // optional
	lastName: String?,
	address: Address?,
	contact: Contact?, // optional
	company: Company?, // optional
	educations: List<Education>,
	) {
	val firstName: String
	val middleName: String? // optional
	val lastName: String
	val address: Address
	val contact: Contact? // optional
	val company: Company? // optional
	val educations: List<Education>
	init {
	if (firstName.isNullOrBlank())
	throw IllegalArgumentException("First name is required")
	if (lastName.isNullOrBlank())
	throw IllegalArgumentException("Last name is required")
	if (address == null)
	throw IllegalArgumentException("Address is required")
	if (educations.isEmpty())
	throw IllegalArgumentException("Education list is required")
	this.firstName = firstName
	this.middleName = middleName
	this.lastName = lastName
	this.address = address
	this.contact = contact
	this.company = company
	this.educations = educations
	}
	class Builder {
	private var firstName: String? = null
	private var middleName: String? = null // optional
	private var lastName: String? = null
	private var address: Address? = null
	private var contact: Contact? = null // optional
	private var company: Company? = null // optional
	private val educations = mutableListOf<Education>()
	fun setFirstName(firstName: String): Builder {
	this.firstName = firstName
	return this
	}
	// OR
	fun setMiddleName(middleName: String) = apply {
	this.middleName = middleName
	}
	fun setLastName(lastName: String) = apply {
	this.lastName = lastName
	}
	fun setAddress(address: Address) = apply {
	this.address = address
	}
	fun setContact(contact: Contact) = apply {
	this.contact = contact
	}
	fun setCompany(company: Company) = apply {
	this.company = company
	}
	fun addEducation(education: Education) = apply {
	this.educations.add(education)
	}
	fun addEducation(educations: List<Education>) = apply {
	this.educations.addAll(educations)
	}
	fun setEducations(educations: List<Education>) = apply {
	this.educations.clear()
	this.educations.addAll(educations)
	}
	fun build(): User {
	return User(
	firstName,
	middleName,
	lastName,
	address,
	contact,
	company,
	educations
	)
	}
	}
	}