Why is Germany allowed to have an army while Japan isn't?

Why is Germany allowed to have an army while Japan isn't?

Quote from the constitution of Japan:
ARTICLE 9. Aspiring sincerely to an international peace based on justice and order, the Japanese people forever renounce war as a sovereign right of the nation and the threat or use of force as means of settling international disputes. (2) To accomplish the aim of the preceding paragraph, land, sea, and air forces, as well as other war potential, will never be maintained. The right of belligerency of the state will not be recognized.

The way this question is phrased seems to imply that somehow each nation is given permission, or not, by another power, presumably the United States, to define their armed forces as an army or not. While in the aftermath of WWII both countries had to agree to basically 'never wage war again' by the victors, namely the United States, since then both nations have regained full autonomy over their own laws. 

In regards to why Article 9 of the Japanese constitution still stands, and why the Japan Defense Force (JDF) is defined as a defense force rather than a military (although it has all the trappings of a military in fact, including military ranks, conventional weapons, and such): Article 9 has come up for frequent debate in the decades since it was implemented in 1950. There are groups in Japan (mainly on the right) who would like to change its status to make it a full military. There are also equally strong voices who would even get rid of the JDF, or any sort of armed forces. Each time the issue has come to the forefront, the current law has stayed. (Prior to March 11 of last year, the prevailing opinion was on the 'get rid of' side, mainly due to seeing maintaining the JDF as a waste of government money. Seeing them in action during the March 11 crisis did a lot to change peoples' minds.) 

In general terms, Japan has had strong pacifist tendencies ever since WWII, so the likelihood of the JDF being redefined as a full military, including the ability to engage in action overseas*, is fairly remote. What could change that speculatively is if North Korea becomes a much larger threat than it is now, or say China or someone decides to get a lot more militarily aggressive, or something along those lines. In other words the political climate in the region has to change quite drastically. (Well, not so drastically maybe in the case of North Korea.) 

To derail a bit, the United States maintains several of their own military bases on Japanese soil (as they do on German soil, and in many other allied countries), although the number has shrunk quite a lot post-Cold War. These include a major navy base in Yokosuka, which is quite close to Tokyo, and a big base in Naha, Okinawa. The latter is a political hot potato, with local residents really, really wanting to kick them off. The current governor of Okinawa was elected largely based on his pledge that he would do everything in his power to get them off the islands. To be cynical and all that, one reason why the U.S. military was so quick and eager to assist in aid efforts post-March 11 was to try to gain political brownie points with the Japanese people to counteract the anti-U.S. military sentiments brought about by the Okinawa base situation.