How resolve this
how change code to get same result
public class myClass
{
List<Drawable> d;
List<Bitmap> b;
public myClass(Integer[] resIDsList)
{
...
}
public myClass(List<? extends Drawable> drawableList) // error occure here
{
d = drawableList;
}
public myClass(List<? extends Bitmap> bitmapList) // and here too
{
b = bitmapList;
}
}
if constructors are same in above?
Define static factory methods, and make the constructor private:
static myClass fromDrawables(List<? extends Drawable> list) {
return new myClass(list, null);
}
static myClass fromBitmaps(List<? extends Bitmap> list) {
return new myClass(null, list);
}
private myClass(List<? extends Drawable> drawables, List<? extends Bitmap> bitmaps) {
// ...
}
(You probably want to add another factory method for the myClass(Integer[]) case; but I hope you get the idea of how to extend the above code for this).
Now you would invoke the factory methods, rather than the constructor:
// Not new myClass(...)
myClass a = myClass.fromDrawables(drawablesList);
myClass b = myClass.fromBitmaps(bitmapsList);
I'd recommend reading Effective Java 2nd Ed Item 1: "Consider static factory methods instead of constructors" for a thorough discussion of this approach.
Due to type erasure, this will not compile. One solution would be to pass the elements to the constructor and simply add them to each respective List.
public myClass(Drawable... drawables) {
d = new ArrayList<>(Arrays.asList(drawables));
}
public myClass(Bitmap... bitmaps) {
b = new ArrayList<>(Arrays.asList(bitmaps));
}
addAll that accepts an array.
List instead.
d = new ArrayList<>(Arrays.asList(drawables)) would be more concise and efficient (it avoids resizing the backing array).You will need to change your List<Drawable> d; to List<? extends Drawable> d; outside of your method. Do this for your List<Bitmap> b; as well. Afterwards, your class should look like this:
public class myClass
{
List<? extends Drawable> d;
List<? extends Bitmap> b;
public myClass(Integer[] resIDsList)
{
...
}
public myClass(List<? extends Drawable> drawableList) // error occurs here
{
d = drawableList;
}
public myClass(List<? extends Bitmap> bitmapList) // and here too
{
b = bitmapList;
}
}
You could also merge both of those constructors into one if you wanted, with this:
public myClass(List<? extends Drawable> drawableList, List<? extends Bitmap> bitmapList)
{
d = drawableList;
b = bitmapList;
}
