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We propose a type system for _object usage analysis_ in Java bytecode (JVML), which verifies the order in which methods of each object are invoked. It is desirable from the viewpoint of both debugging and security that objects in a program are used in valid manners, i.e., according to the intention of the programmer or the library provider. For example, we expect that a File object is first created and initialized, then opened before read or written, and finally closed (and no more used after that). The current verifier of JVML, however, does not check such validity of object usage. To improve this situation, we construct a type system for analyzing object usage in JVML, adopting three key ideas from Kobayashi et al.'s generic type system for pi-calculus, object locking analysis for JVML, and resource usage analysis for lambda-calculus. The first key idea is to extend the type of an object with its _usage_, information about how the object is going to be used (specifically, the order in which methods of the object are invoked). The second is to extend type environments so that they keep track of the usage information even across different variables, in order to deal with aliases. The third is to treat write and read operations on object fields (putfield and getfield) as usage of the object, in order to handle destructive updates.