Japan is a pluralist democracy ruled by law. China is a one party state. Japan is no threat to any nation. China threatens all nations in east Asia.
The USA chooses to share its military technology with Japan (Aegis, now possibly the F35) as Japan is a trusted ally. The USA does not share these with China or Korea.
Abe is right to lay down the law. Any attempt by China to occupy Japanese Territory will be an act of war. If China starts a war in East Asia, the USA will be involved.