An updated version of this demonstration, without Java, is available here.
This applet draws numerical approximations to the solution of the differential equation
with initial condition x(0) = 100 using either Euler's method or a Runge-Kutta method of order 2. The initial step size is 5. The step size may either be cut in half or doubled by clicking on the appropriate button. Changing methods will reset to the initial step size. The curve drawn in green is the exact solution,