Resistivity and Current Density

A conductor of length $0.15\ \mathrm{m}$ and resistivity $\rho = 4.0 \times 10^{-7}\ \Omega \cdot \mathrm{m}$ is subjected to a potential difference of $12\ \mathrm{V}$ across its length. What is the magnitude of the current density $J$ in the conductor?