public class Circle implements Form, Transformable { private double diameter; public Circle(double d) { if ( d <= 0) { System.out.println("Circles must hace a positive diameter, bye!"); System.exit(1); // un peu dur ! } diameter=d; } public double getDiameter() { return diameter; } public double perimeter () { return Math.PI*diameter ; } public double area() { return Math.PI*diameter*diameter/4; } public void enlarge(double factor) { if (factor > 0) diameter *= factor; else System.err.println("impossible to enlarge with a non positive factor"); } public String toString() { return "Circle("+diameter+")"; } }