Class subclass type with a public method - kotlin

Question

I don't understand why in Subclass definition a public method is involved
class ViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView)
Source code of the RecyclerView.ViewHolder
public abstract static class ViewHolder {
public ViewHolder(View itemView) {
if (itemView == null) {
throw new IllegalArgumentException("itemView may not be null");
}
this.itemView = itemView;
}

Answer 1

Your question is why does the following code appear to call a public method ViewHolder within RecylcerView. Here is your code, with a slight rename to make things clearer:
class MyClass(itemView: View) : RecyclerView.ViewHolder(itemView)
And what is missing from your description is showing the outer class:
class RecyclerView { // outer/containing class
static class ViewHolder { // nested class
public ViewHolder(ViewItem view) { // constructor
// ... constructor body
}
}
}
Now looking at that nesting, to talk about the ViewHolder class you need to reference it as RecyclerView.ViewHolder. Then if you want to construct an instance of that you must add the constructor parameters, for example in Java:
new RecyclerView.ViewHolder(view);
In Kotin when you descend from a class, your constructor must call the super constructor and the short hand for that is to do it in the declaration.
class MyClass(ViewItem view) : RecyclerView.ViewHolder(view) {
// ...class body
}
This says MyClass descends from ViewHolder which is a nested class of RecyclerView and the constructor parameter coming into MyClass constructor is being passed into the super constructor of ViewHolder.
This is the same as Java:
class MyClass extends RecyclerView.ViewHolder {
public MyClass(ViewItem view) {
super(view);
}
}
You can also import the nested static class directly, then drop the RecyclerView prefix, but it is a bit clearer to leave it.