On which platform does Java not run?

Windows. Note: As of April 8, 2014 Microsoft stopped supporting Windows XP and therefore it is no longer an officially supported platform. Users may still continue to use Java 7 updates on Windows XP at their own risk, but support will only be provided against Microsoft Windows releases Windows Vista or later.

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What is cross-platform development?

Cross-platform mobile development is the creation of software applications that are compatible with multiple mobile operating systems . Originally, the complexity of developing mobile apps was compounded by the difficulty of building out a backend that worked across multiple platforms.

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