如何在Kotlin的数据类上实现Null Object模式? [英] How to implement Null Object pattern on data class in Kotlin?
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问题描述
我有一个Kotlin数据类:
I have a Kotlin data class:
data class PaymentAccount(
val accountId: Int,
val accountNumber: String,
val title: String
)
这是我在Java中要做的:
This is what I'd do in Java:
创建一个抽象类:
public abstract class PaymentAccount {
protected int accountId;
protected String accountNumber;
protected String title;
public PaymentAccount(int accountId,
String accountNumber,
String title) {
this.accountId = accountId;
this.accountNumber = accountNumber;
this.title = title;
}
}
创建空对象并扩展抽象类:
Create null object and extend abstract class:
public class NullPaymentAccount extends PaymentAccount {
public NullPaymentAccount() {
super(-1,
"Invalid account number",
"Invalid title");
}
}
创建一个真实的对象并扩展抽象类:
Create a real object and extend abstract class too:
public class RealPaymentAccount extends PaymentAccount {
public RealPaymentAccount(int accountId,
String accountNumber,
String title) {
super(accountId,
accountNumber,
title);
}
}
如何在Kotlin中正确实现Null Object模式?有不止一种方法吗?如果是这样,最简洁,最优雅的方法是什么?
How to implement Null Object pattern in Kotlin properly? Is there more than one way? If so, what is the most concise and elegant way?
推荐答案
在Kotlin中,您可以执行相同的操作,而只需更少的代码行:
In Kotlin you can do the same, just with less lines of code:
interface Account {
val accountId: Int
val accountNumber: String
val title: String
}
object EmptyAccount : Account {
override val accountId: Int = 1
override val accountNumber: String = ""
override val title: String = ""
}
data class PaymentAccount(
override val accountId: Int,
override val accountNumber: String,
override val title: String): Account
请注意,为了提高效率,我们也将EmptyAccount
单调.
Notice that we also make EmptyAccount
singletone for efficiency.
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