The StampedLock class has some sample code with a distanceFromOrigin() method. The sample code uses

return Math.sqrt(currentX * currentX + currentY * currentY);

to compute the Euclidean distance. From a numerical perspective, this would be better computed using Math.hypot or StrictMath.hypot. The hypot method "Returns sqrt(x^2 +y^2) without intermediate overflow or underflow."