Understanding how actually drawRect or drawing coordinates work in Android

Question

I am trying to draw a rectangle over a canvas and I am facing troubles to understand the in-depth of rectangle draw of Android. I\'ve read tutorials and every possible but I

Answer 1

This will make sense.

float left = 100, top = 100; // basically (X1, Y1)

float right = left + 100; // width (distance from X1 to X2)
float bottom = top + 100; // height (distance from Y1 to Y2)

Thus

RectF myRectum = new RectF(left, top, right, bottom);
canvas.drawRect(myRectum, myPaint);