Java-ArrayList <E> 功能参数

Question

I wanted to use a function that used a arraylist for multiple types of arraylists, but I don't know how to do that.

ArrayList<TextView> List2 = new ArrayList<>();
ArrayList<View> List1 = new ArrayList<>();

ChangeTextSize(List1);
ChangeTextSize(List2);

public void ChangeTextSize(ArrayList List){
        for (int i = 0; i < List.size(); i++){
            List.get(i).setTextSize(TypedValue.COMPLEX_UNIT_SP,15);
   }
}

-Edit: The function is meant for any view. I'm now aware that setTextSize isn't allowed for view.

Answer 1

If you want to change the text size using the function setTextSize the object which you call the function on has to be a TextView because that object has the function . A View doesn't have the function setTextSize so that won't work.

But if you have a function that both TextView and View have; for example setBackgroundColor you can do it like this:

public void changeBackgroundColor(ArrayList<? extends View> list) {
  for (View v: list) {
    v.setBackgroundColor(Color.red);
  }
}

So basically you give your list argument a generic; meaning in this case: "all the element in the list should be a view or sub-class thereof". So the methods you can call on the element from this list are all methods available in the View class.

But if you want to change text-sizes your function needs to accept a list of TextView (or sub-classes thereof), like this:

public void changeTextSize(ArrayList<? extends TextView> list) {
  for (TextView tv: list) {
    tv.setTextSize(TypedValue.COMPLEX_UNIT_SP,15);
  }
}

Answer 2

Is this Android?

You can use a wild card to allow a range of type-parameters. Something like:

public void ChangeTextSize(ArrayList<? extends TextView> list){
        for (int i = 0; i < list.size(); i++){
            list.get(i).setTextSize(TypedValue.COMPLEX_UNIT_SP,15);
   }
}

But I don't see that View has a method setTextSize so obviously that type can't be used here.