Java 检查null时的惯用Kotlin
在Java中,我会这样做:Java 检查null时的惯用Kotlin,java,kotlin,idioms,Java,Kotlin,Idioms,在Java中,我会这样做: class Person { private Record record; public String name() { record().get("name"); } private Record record() { if (record == null) { refetch(); } return record; } private void
class Person {
private Record record;
public String name() {
record().get("name");
}
private Record record() {
if (record == null) {
refetch();
}
return record;
}
private void refetch() {
record = service.doSomething()
}
}
internal class Record(var name: String, var address: String)
internal class Person {
private var record: Record? = null
fun name(): String {
return record()!!.name
}
private fun record(): Record? {
if (record == null) {
refetch()
}
return record
}
private fun refetch() {
record = Record("Joe Smith", "101 Broadway, NYC, NY")
}
}
在Kotlin中,我有一个等效代码:
class Person(private var record: Record?) {
fun name() : String {
record().get("name");
}
private fun record() : Record {
record ?: refetch()
return record!!;
}
private fun refetch() {
record = service.doSomething()
}
}
如您所见,我正在使用代码>接线员,我真的不喜欢。还有其他更惯用的方法吗
如果我简单地遵循Java方式(If(record==null)
),我会得到以下错误:
智能转换为“记录”是不可能的,因为“记录”是可变的
此时可能已更改的属性
在惯用的Kotlin中,您将使用:
你是Java代码没有编译,所以我模拟了一个例子
class Record {
String name;
String address;
Record(String name, String address) {
this.name = name;
this.address = address;
}
String getName() {
return name;
}
}
class Person {
private Record record;
public String name() {
return record().getName();
}
private Record record() {
if (record == null) {
refetch();
}
return record;
}
private void refetch() {
record = new Record("Joe Smith", "101 Broadway, NYC, NY");
}
}
Kotlin强制您在定义某个值时使用“?”字符来声明该值是否可为null。所以它需要像这样:
class Person {
private Record record;
public String name() {
record().get("name");
}
private Record record() {
if (record == null) {
refetch();
}
return record;
}
private void refetch() {
record = service.doSomething()
}
}
internal class Record(var name: String, var address: String)
internal class Person {
private var record: Record? = null
fun name(): String {
return record()!!.name
}
private fun record(): Record? {
if (record == null) {
refetch()
}
return record
}
private fun refetch() {
record = Record("Joe Smith", "101 Broadway, NYC, NY")
}
}
为什么对空安全类型使用空检查?可能是@Zoe的重复项抱歉,我错过了?
。在Kotlin中,您将使用一个延迟初始化的委托属性:谢谢。如何强制重新初始化?i、 e.再次调用'service.doSomething()。这可能吗?好吧,stdlib中没有这样的功能。您需要自己实现一个ResettableLazy。一个快速的谷歌搜索结果是:非常感谢。我会的。