At noon in Japan, we usually eat at school. Most schools don't have supermarkets and canteens, some schools do, and some schools don't. Generally, universities and society have canteens. The best choice is to have lunch at school.
In ordinary high schools in China, the lunch break is between one and a half hours and two hours. If the home is near, you can go home for lunch and sleep. In Japan, high schools finish their studies early. If lunch break is included, it will take about an hour. Most schools have a break of less than an hour, and only 50 minutes at most.
What Japan values most is food safety. Every generation pays more attention to food safety. China is not so particular about food, nor so strict about Japanese food. In China, it is common to eat something while eating. Some meals in China are not nutritious, while Japanese lunches are nutritious.