  In the last years different studies have revealed the usefulness of a
microcanonical analysis of finite systems when dealing with phase transitions.
In this approach the quantities of interest are exclusively expressed as
derivatives of the entropy $S = \ln \Omega$ where $\Omega$ is the density of
states. Obviously, the density of states has to be known with very high
accuracy for this kind of analysis. Important progress has been achieved
recently in the computation of the density of states of classical systems, as
new types of algorithms have been developed. Here we extend one of these
methods, originally formulated for systems with discrete degrees of freedom, to
systems with continuous degrees of freedoms. As an application we compute the
density of states of the three-dimensional XY model and demonstrate that
critical quantities can directly be determined from the density of states of
finite systems in cases where the degrees of freedom take continuous values.
