I understood, I think, that a \"Bean\" is a Java class with properties and getters/setters. As much as I understand, it is the equivalent of a C struct. Is that true?
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Java Beans is a standard, and its basic syntax requirements have been clearly explained by the other answers.
However, IMO, it is more than a simple syntax standard. The real meaning or intended usage of Java Beans is, together with various tool supports around the standard, to facilitate code reuse and component-based software engineering, i.e. enable developers to build applications by assembling existing components (classes) and without having to write any code (or only have to write a little glue code). Unfortunately this technology is way under-estimated and under-utilized by the industry, which can be told from the answers in this thread.
If you read Oracle's tutorial on Java Beans, you can get a better understanding in that.