“Java” is a word for “OO” (Object Oriented) concept in the eyes of Java2Script. C++ is considered not a pure OO language, but C# may be. And there are other OO languages. But the well-known one should be Java. Java2Script just takes Java as a great OOAD tool (language tool) to analyze, design and implement desktop applications or rich client platform (RCP).
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We do not care what languages are used. We know we use OO concepts to design things and get what we want by using the existed tools.