A question of knife legality in Europe

Me and my brother will be backpacking in Europe for a month and well be in the following countries: Germany, Italy, Netherlands, Belgium, France, and Switzerland. My question is, does anyone know the legality of carrying a folding knife for purposes of self defense? Is there a size limit? Do any of these countries ban it outright?

I ask because we will be staying in the cheapest hostels we can find the whole time and as a result may be in some rougher neighborhoods.

Thank you for your input!

I tried a google search but came up with little