Review

class RealVector {
    /**
     * Returns the L<sub>1</sub> norm of the vector.
     * <p>The L<sub>1</sub> norm is the sum of the absolute
     * values of the elements.</p>
     *
     * @return the norm.
     * @see #getNorm()
     * @see #getLInfNorm()
     * @see #getL1Distance(RealVector)
     */
    public double getL1Norm() {
        double norm = 0;
        Iterator<Entry> it = iterator();
        while (it.hasNext()) {
            final Entry e = it.next();
            norm += FastMath.abs(e.getValue());
        }
        return norm;
    }
}

class RealVector {
            @Override
            public double getL1Norm() {
                return v.getL1Norm();
            }

}