在kotlin中创建新的泛型类实例的正确方法是什么? [英] What is the proper way to create new instance of generic class in kotlin?
问题描述
val entityClass = javaClass< Class< T>>()
var entity = entityClass.newInstance()。newInstance()
但它是错误的并且导致 IllegalAccessException
on java.lang.Class.newInstance(Class.java:1208)
Class< c $ c>类<字符串>>
。我不确定这是你想要的。在第2行中,您首先创建了一个 Class
实例,然后是 T
中的一个,但无论如何这是不可能的,因为有关 T
的通用信息在运行时会丢失。除此之外,您不能直接实例化类对象。 解决方案
一种可能的解决方案是添加一个类型为 Class
的参数添加到您的函数或类中,并用它来实例化这样的对象。
fun< T> foo(entityClass:Class< T>){
var entity:T = entityClass.newInstance()
}
fun test(){
foo(Object: :class.java)
}
但实际上有一个更优雅的解决方案,反射。定义方法类型的参数() - > T
并使用构造函数引用。 这里是我的相关问题关于构造函数的参考,这里是代码:
fun< T> foo2(factory:() - > T){
var entity:T = factory()
}
fun test(){
foo2对象)
}
I use following initialization:
val entityClass = javaClass<Class<T>>()
var entity = entityClass.newInstance().newInstance()
but it's wrong and causes IllegalAccessException
on java.lang.Class.newInstance(Class.java:1208)
If you let IntelliJ add explicit type information, you see that entityClass
is actually of type Class<Class<String>>
. I'm not sure if that's what you want. In line 2 you are first creating an instance of Class<T>
and then one of T
but that's not possible anyway, because the generic information about T
is lost at runtime. Apart from that you can't instantiate class objects directly.
Solution
One possible solution would be to add a parameter of type Class<T>
to your function or class and use it to instantiate objects like this.
fun <T> foo(entityClass: Class<T>) {
var entity: T = entityClass.newInstance()
}
fun test() {
foo(Object::class.java)
}
But there's actually a more elegant solution without the use of reflection. Define a parameter of method type () -> T
and use constructor references. Here's my related question about constructor references and here's the code:
fun <T> foo2(factory: () -> T) {
var entity: T = factory()
}
fun test() {
foo2(::Object)
}
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