From OpenGL docs:
The SHININESS parameter is a value that specifies the RGBA specular exponent of the material. Only values in the range [0,128] are accepted.
From Java3D docs:
Shininess - the material's shininess, in the range [1.0, 128.0] with 1.0 being not shiny and 128.0 being very shiny. Values outside this range are clamped. The default value for the material's shininess is 64.
For Xith3D, the valid range is [0, 128] and default is 64.
If you specify something different, it will be passed directly to OpenGL.