Create a generic method to match the interface and main parent class
I have the following method:
private void setFilledAndAdd(Shape obj, Color col, int x, int y) {
obj.setFilled(true); // needs interface Fillable
obj.setFillColor(col);
add(obj, x, y); // needs children of Shape (or Shape itself)
}
If I add one of the lines:
setFilledAndAdd(oval, color, x, y);
Compile time error on line obj.setFilled(true);
and line obj.setFillColor(col);
. Because Shape
not Fillable
. Undefined for the Shape type.
Changing the type of an argument in a method setFilledAndAdd
to Fillable
(not Shape
) results in a compile-time error on the line add(obj, x, y);
. In this case, he needs Shape
.
All the kids Shape
I use are Fillable
. Give me a hint on how to get this method to work.
Thank.
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You can use generics to say that you expect an object with two characteristics
private <T extends Shape & Fillable> void setFilledAndAdd(T obj, Color color, int x, int y){
obj.setFilled(true); // needs interface Fillable
obj.setFillColor(color);
add(obj, x, y);
}
private void add(Shape s, int x, int y){
// whatever code you have goes here.
}
This compiles fine for me.
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If you have control over the source Shape
and Fillable
, I would just rewrite so that all shapes are filled if possible. You could also use public abstract class FillableShape extends Shape implements Fillable
to keep using the type system.
Otherwise, you can use type-casting with runtime checking to make sure the form is complete:
if(obj instanceof Fillable){
((Fillable) obj).setFilled(true);
((Fillable) obj).setFillColor(col);
add(obj, x, y);
} else {
// show an error message or something
// (or just draw the shape without filling it, if you want)
}
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