Addressing the question by MigLeader regarding why Japan has not developed its own indigenious fighter designed for Island defense...
First of all you have to consider what Japan's military forces are for. Obviously they have no intention or desire to invade other countries (Let's put WWII behind us) so as their name implies, the military is for Self Defense.
So what are the potential threats to Japan? Let's make it simple... Naval or Air threats. (I'll put aside ground forces for now, if a hostile army has gotten to Japanese soil then something's seriously f*cked up)
The main conceivable potential threats to Japan would in all likelihood would be North Korea or China. (I'll dismiss politics here, I'll just say they are the most likely, however unlikely it is, for the sake of argument otherwise this would get old quick)
The JMSDF has a highly professional submarine force that is proficient in anti-submarine as well as anti-surface work. They are also a force that complements the surface fleet; the JSMDF does work on coordinated ship-sub-aircraft operations. Japan has Harpoons as well as a small variety of Anti-Ship missiles, I wouldn't consider them too overrated in terms of Anti-Ship capability.
Considering anti-air capabilities, though...
While JASDF units have a high professional reputation, and have increased their exercise participation with U.S. air forces in recent years, in weaponry they would today enter combat with PLA fighters at a potential disadvantage. Japan is (probably) examining the purchase of a new air-superiority fighter to succeed its 70 or so F-4EJ fighters. They might be considering the purchase of the F/A-22 and the F-35, even though the later would not be available until after 2013.
I know this is really simple, but I'm kind of tired... I'll add more to this later...
Even with a future Chinese superiority, however Japan still has the defender's advantage of location, familiarity of surrounding terrain, and SAMs. The defender has the advantage of easier to coordinate logistics, which is a big plus in war.
I would say that as of now the Japanese Self Defense Force fills its role pretty well. They don't need a fighter designed for island defense because they already have one/some, the F-15J and its supporting aircraft. To defend your island you need anti-air and anti-ship capable aircraft, and that's what Japan's good at.
I don't think they could stop potential missile strikes from North Korea or China, but that's another story... even the US can't confidently stop missile strikes... "Star Wars" is obviously a possibility but the Japanese are smarter than to waste money on it...