In spite of planning for over 60 years, China is incapable of invading Taiwan a mere 90 miles away. They lack the Naval strength to traverse the straight without being wiped out by missiles, aircraft and submarines.
An attack on Japan would be impossible
Anytime China decided to attack Taiwan she could. She would also suffer tremendous losses but when you have a billion people that's not a issue. The reason why China hasn't bothered is because they have been quietly converting the people over to their side for a long time. In the next 20 years or so Taiwan will beg to be let back into the fold.
Japan, on the other hand is a different challenge. That's why China has been developing a blue water navy. She has been waiting for a weak POTUS, like the one in office, so that if they decide to act...we won't.
They are weighing the pro's and cons of an attack to take the islands right now. How much western money will they lose if they decide to go. Is it worth the financial hit to do it. When those numbers pencil out, they'll move, and ain't no one going to stop them.