Nope, what that does is accepts a double from the input, and creates a new instance of Circle providing it with that double.
The only way to modify it (such as taking the radius from another class), is to construct a new instance of circle since there is currently no way to mutate the value of the radius. So if you wanted to create a new circle twice the size of an existing circle, you can use the get method on it:
Circle doubleSizeCircle = new Circle(smallerCircleInstance.getRadius());. Now, the current class definition you have for Circle has a package level access to the variables, but I always assume that the variables will be private unless its final.
Edit:
To expand a bit, since the scope of your current circle's radius property is package accessible, you can actually modify it directly:
PHP Code:
Circle c = new Circle();
c.radius = 4.2;
However, this is not the most ideal since it would also allow me to do:
PHP Code:
c.radius = -4.2;
which is not a valid raidus.