Have you ever thought about your mobile phone security ? Probably not, and this is because too many devices phones have limited features so they don't support 3rd party applications to get viruses. Neither java application helps the virus creators. Java creates a virtual machine on the phone, so if that something bad happens it will stay into that virtual machine, he can't access other parts of your phone.
What about smartphones ? Are they vulnerable to viruses ? The smartphone creators are much more careful about security, they really invest some time in it, but that can't ensure that the viruses will never come.
Why they are making viruses for mobile phones ? People are checking their e-mail with the phone, people are paying with the mobile phone, it contains very sensitive informations, so the virus creators hardly wait that more people will start using smartphones.
You can't compare a smartphone secirity with a windows one, but a smartphone is open 24/24, when you go to shop, they try to give you their catalog trough bluetooth, maybe it is the good one. Other big shops have apps so you can do something funny, but someday you will donwload the wrong thing. Also the hackers might find software vulnerabilities and they can do some damage without you downloading anything.
Maybe now too few people have smartphones for the virus creators to care about, but a protection is always good.
There are already malwares created for mobile phones. It seems that they can't do much damage now, but you are never too protected.
Anti-virus creators started to solve this problem and they launched anti-virus for mobiles. I strongly recommend
Kaspersky Mobile Security , they pay real attention to security.