Java creators tried to avoid giving developers any sharp edges. Interactions between signed and unsigned integers can be surprising, so they disallowed unsigned integers.

Of course, not having access to unsigned quantities makes interaction with other programs difficult :(

The one that annoys me is that people think implicit type conversions are dangerous for some reason, so they also disallowed `char a = 10; short b = a;` without writing a cast even though this makes no sense.