/** 
 * Line - model a line
 */

public class Line {

    private double x1;
    private double y1;
    private double x2;
    private double y2;
    
    /**
     * Line - a line in the first quadrant (made up example)
     * @require both points (x1,y1) and (x2, y2) to be in first quadrant
     */
    public Line(double x1, double y1, double x2, double y2) {
        this.x1 = x1;
        this.y1 = y1;
        this.x2 = x2;
        this.y2 = y2;
        assert x1 >= 0 && y1 >= 0 && x2 >= 0 && y2 >= 0 :
            "A point is not in RHQ";
    }
    
    public double length() {
        return Math.sqrt( (x2-x1)*(x2-x1) + (y2-y1)*(y2-y1) );
    }
    
    public static void main( String[] args ) {
        
        Line l = new Line(0.,0.,10., -10.);
        System.out.println( "No assertions" );
    }
}