Tuple2D extends Point2D.Double implements ILocated2D { public Tuple2D mult(double i) { return new Tuple2D(x * i, y * i); } Tuple2D(double x, double y); boolean isZero(); double length(); Tuple2D normalize(); double angle(); Tuple2D midpoint(Tuple2D position); Tuple2D add(Tuple2D position); Tuple2D sub(ILocated2D rhs); Tuple2D mult(double i); Tuple2D div(double i); Tuple2D getPosition(); Tuple2D rotate(double radians); double distance(ILocated2D other); @Override String toString(); double angleBetweenTargets(ILocated2D a, ILocated2D b);  }
@Test public void testMult() { Tuple2D test = new Tuple2D(2, 3); test = test.mult(2); assertEquals(test.x, 4, ERROR); assertEquals(test.y, 6, ERROR); }