I know Asia is a poverty stricken continent but I am planning to visit Japan, Hong Kong and Singapore this summer. I have heard yakuza in Japan, triads in Hong Kong and pirates in Singapore. Are beggars a big problem over there? Would my life be in danger?

I would like to visit South Africa one day on a tour. I would like to visit Johannesburg, Pretoria, Cape Town and Durban. However, I met a South African couple who said that it is not very safe and sometimes strangers can knock on your door and rob you and threaten you with a gun. Is this true? Is South Africa a dangerous place? Or only certaina areas? Are the police effective or corrupt?
What about those cities I mentioned?