### Question:
PolynomialFunction2D implements Function2D, Serializable { @Override public int hashCode() { return HashUtilities.hashCodeForDoubleArray(this.coefficients); } PolynomialFunction2D(double[] coefficients); double[] getCoefficients(); int getOrder(); @Override double getValue(double x); @Override boolean equals(Object obj); @Override int hashCode();  }### Answer:
@Test public void testHashCode() { PolynomialFunction2D f1 = new PolynomialFunction2D(new double[] {1.0, 2.0}); PolynomialFunction2D f2 = new PolynomialFunction2D(new double[] {1.0, 2.0}); assertEquals(f1.hashCode(), f2.hashCode()); }