That's the clue to the whole disvussion. I say nothing changed but everyone here writes that's a great strategic move by Chinese government.
... Is it not?
If they claimed the ADIZ as national airspace or something that would be completely illegal.
But claiming an ADIZ is a great strategic move because:
1: Such an ADIZ will encompass the disputed islands, eroding Japanese sovereignty over it
2: It puts the ball in Japan's court as to how to respond. If they don't shoot down any PLAAF fighters over Diaoyu/senkaku airspace they are effectively forfeiting a significant part of what constitutes sovereignty. If they do shoot, then they will be clearly seen as the aggressors.
3: Japan, and the US both have their own ADIZ which are much larger than China's, so they do not have any grounds to protest over it.
I don't understand the rant on Japanese government as those are your words, not Japanese government...
Yes, but the Japanese government and media always "voice concern" over increasing passages of both Chinese and Russian aircraft (and ships) through international airspace and waters near its own. What's between the lines is that there seems to be a Japanese assumption that exists that they hold some level of control in their ADIZ or that if countries enter that space then it is somehow a threat to Japan.
Unfortunately, there are gems underwater which wait to be brought up on the surface in lots of those places... And why China needs so much space there? To have a pond there and operate their fleet there?
I'd say it's two sided.
1: USN/JASDF planes may conduct surveillance operations which need to be monitored. This is standard practice for many nations and the US itself has had a massive ADIZ for years, but PRC until yesterday didn't have an institutionalized ADIZ.
2: the Diaoyu territorial dispute/Japan's large ADIZ. By creating China's own ADIZ it can challenge Japanese sovereignty over Diaoyu while also exerting a greater air power presence.