I suppose that's something every Java programmer should know: How types are automatically converted during "arithmetic" operations. There are some subtleties (like byte+short => int), but it's not too much to remember.

The deeper question is: Was it a wise choice to disallow operator overloading BUT use "+" as a string concatination operator AND convert all values to strings during string concatenation?

I think not, but it's a rather moot point, since that desing decision is not likely to change...