  Sun and the CERT recommend for secure Java development to not allow partially
initialized objects to be accessed. The CERT considers the severity of the
risks taken by not following this recommendation as high. The solution
currently used to enforce object initialization is to implement a coding
pattern proposed by Sun, which is not formally checked. We propose a modular
type system to formally specify the initialization policy of libraries or
programs and a type checker to statically check at load time that all loaded
classes respect the policy. This allows to prove the absence of bugs which have
allowed some famous privilege escalations in Java. Our experimental results
show that our safe default policy allows to prove 91% of classes of java.lang,
java.security and javax.security safe without any annotation and by adding 57
simple annotations we proved all classes but four safe. The type system and its
soundness theorem have been formalized and machine checked using Coq.
