Java Circle-Circle Collision Detection

Question

Here is the circle class:

public class Circle {
    private double radius;

    private double x;
    private double y;
}

How can I tell if two objects from this class (circles) are colliding?

P.S. Can you use the method that avoids taking a square root?

Answer 1

double xDif = x1 - x2;
double yDif = y1 - y2;
double distanceSquared = xDif * xDif + yDif * yDif;
boolean collision = distanceSquared < (radius1 + radius2) * (radius1 + radius2);