F-35 Weapons Pylons
Andy Wolfe/US Navy
The F-35 highlighting its weapons pylons.

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Japan, guided by fiery nationalist Prime Minister Shinzo Abe, has committed to purchasing 42 F-35As with the possibility of ordering more in the future. 
Although the F-35 has had a controversial run in the U.S. due to problems with design and manufacturing and a history of going over budget, Japan sees the fifth-generation fighter as a key deterrent against the rising militancy of China. 
Beijing, for its part, appears to have a strong case of jet envy. China's state owned Global Times tabloid said the F-35 is the worst nightmare for its Liaoning aircraft carrier, according to Taiwan's Want China Times.
That article was based on a claim in Canada's Kanwa Asian Defense that F-35s could strike the Liaoning with hard-to-intercept joint strike missiles from a safe distance of 290km. The F-35 should also be able to locate and engage China's main aircraft, the J-15, before the F-35 is even detected.
For comparison, China's J-15 carries air-to-ship missiles that have a range of only 180km.
China is also developing a fifth-generation fighter, the Chengdu J-20. The J-20 is meant to be a multi-role stealth aircraft, similar in scope to the F-35. However, this is China's first attempt at building a stealth aircraft. As such, each of the three released prototypes of the J-20 differ substantially as the Chinese learn from their own designs what makes the craft functional.
In terms of absolute stealth, the F-35 has an advantage over the J-20's design as it has a significantly lower noticeable radar cross-section. The F-35' radar technology has a major advantage, too. The F-35 should be able to locate the J-20 due to its large fuselage and canard before it itself is detected.  
Due to Japan's access to high quality military equipment, Dr. Larry M. Wortzel, the president of Asia Strategies and Risks, insists that Japan is the strongest military power in the Pacific.
"Japan has the strongest navy and air force in Asia except for the United States," he said at during a presentation at the Institute of World Politics last September. "The most modern, the most effective. They're still restricted by Article 9 of the Constitution, which forever renounces war as a sovereign right of the nation ... but you don't want to mess with them."
Japan is planning on using the F-35, which should start being delivered to Japan in the coming years, as a front-line air defense fighter. The jet should start arriving in Japan in 2017.