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    <p>In short, it's perfectly safe.</p> <p>Since Java 6, Oracle's compiler has made class files with a StackMapTable. The basic idea is that the compiler can explicitly specify what the type of an object is, instead of making the runtime do it. That provides a tiny speedup in the runtime, in exchange for some extra time during compile and some complexity in the compiled class file (the aforementioned StackMapTable). </p> <p>As an experimental feature, it was not enabled by default in the Java 6 compiler. The runtime defaults to verifying the object types itself if no StackMapTable exists.</p> <p>Until Java 7. Oracle made it mandatory: the compiler generates them, and the runtime verifies them. It still uses the old verifier if the StackMapTable isn't there... but only on class files from Java 6 or earlier (version 50). Java 7 class files (version 51) are required to use the StackMapTable, and so the runtime won't cut them the same slack.</p> <p>That's only a problem if your classfiles were generated without a StackMapTable. For instance, if you used a non-Oracle JVM. Or if you messed with bytecode afterwards -- like instrumenting it for use with a debugger, optimizer, or code coverage analyzer. </p> <p>But you can get around it! Oracle's JVM provides the -XX:+UseSplitVerifier to force the runtime to fallback to the old type verifier. It doesn't care about StackMapTable.</p> <p>In practice, the hoped-for optimization in runtime speed and efficiency hasn't materialized: if it exists, it hasn't been enough for anyone to notice. As the new type verifier doesn't provide any new features (just the optimization), it's perfectly safe to shut it off. </p> <p>Oracle's explanation is at <a href="http://www.oracle.com/technetwork/java/javase/compatibility-417013.html" rel="noreferrer">http://www.oracle.com/technetwork/java/javase/compatibility-417013.html</a> if you search for JSR 202.</p>
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