In this paper, we describe static analysis techniques for finding bugs in programs using the Java Native Interface (JNI). The JNI is both tedious and error-prone because there are many JNI-specific mistakes that are not caught by a native compiler. This paper is focused on four kinds of common mistakes. First, explicit statements to handle a possible exception need to be inserted after a statement calling a Java method. However, such statements tend to be forgotten. We present a typestate

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... is to detect this exception-handling mistake. Second, while the native code can allocate resources in a Java VM, those resources must be manually released, unlike Java. Mistakes in resource management cause leaks and other errors. To detect Java resource errors, we used the typestate analysis also used for detecting general memory errors. Third, if a reference to a Java resource lives across multiple native method invocations, it should be converted into a global reference. However, programmers sometimes forget this rule and, for example, store a local reference in a global variable for later uses. We provide a syntax checker that detects this bad coding practice. Fourth, no JNI function should be called in a critical region. If called there, the current thread might block and cause a deadlock. Misinterpreting the end of the critical region, programmers occasionally break this rule. We present a simple typestate analysis to detect an improper JNI function call in a critical region. We have implemented our analysis techniques in a bug-finding tool called BEAM, and executed it on opensource software including JNI code. In the experiment, our analysis techniques found 86 JNI-specific bugs without any overhead and increased the total number of bug reports by 76%.