You are going to constantly need to check the coordinates to make sure
they are in bounds (in the canvas) before you draw.
It is going to get tedious to keep saying if (x>100 && x<400 && y>100 & y<400 && x2...)
We might write a function (same as method) to check if we are in bounds:
public boolean isInCanvas(int x, int y)
//check x and y make sure its in canvas
return true if in canvas
return false otherwise
now before we draw we would say something like
if (isInCanvas(x,y) && isInCanvas(x2,y2))
//that would mean that both x,y and x2,y2 are in the canvas region.