We present a type-based analysis ensuring memory safety and object protocol completion in the Java-like language Mungo. Objects are annotated with usages, typestates-like specifications of the admissible sequences of method calls. The analysis entwines usage checking, controlling the order in which methods are called, with a static check determining whether references may contain null values. It prevents null pointer dereferencing and memory leaks and ensures that the intended usage protocol of every object is respected and completed. Moreover, the type system admits an algorithm that infers the most general usage wrt. a simulation preorder that makes a class declaration well-typed. It has been implemented in the form of a type checker and a usage inference tool.