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So here's a story of, by far, the weirdest bug I've encountered in my CS career.
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This is a most excellent place for technology news and articles.
Java was giving a no such method exception at runtime, but it compiled fine. Granted, that method was recently added to the class, but it was pretty simple and again, you'd expect the compiler to detect things like that.
Turns out the code I inherited from a not-great team had that class in two different places. Maven replaced the one I worked on with the untouched copy, which went into the build.