I think it is important to make it known for anybody who might not be familiar with the country that Japan DNE Tokyo and Tokyo DNE Japan. While credit card usage is becoming really common in Tokyo and a few other urban centers, it has yet to catch on everywhere else.
Just for the sake of example: In the city where I live, I can use credit cards at Lawson convenience stores (7-11, however, famously does not accept credit cards for purchases, although their ATMs are able to handle them for cash advances) and, if I go into the station ticket office, I can purchase train tickets with credit. The vending machines, however, only accepts cash, as do most businesses in town, save for the supermarkets and department stores. Also, of the 13 train stations in town, only the largest in the center of town takes credit, the others only have the facilities to take cash.
Large chains tend to accept credit, but in many areas, like my own, those large chains are very few in number. If I eat at Gusto, a nationwide family restaurant chain specializing in mediocre meals and so-so service, I can pay with credit. However, if I eat at Issaku, a large, locally-owned and operated izakaya (think like a bar & grill) that is otherwise incredibly modern, down to a computerized ordering system, I can pay only with cash. The same goes for almost any other restaurant or bar in town. If I asked to use credit for a taxi, I’d probably be laughed out of the cab. In the future this may change, but, for the time being and for better or for worse, credit cards have not yet caught on all over in the same way they have in Tokyo.
Perhaps a good rule of thumb in Japan is, generally, if you can reasonably expect to pay more than 10,000 yen at a place by yourself, it becomes much more likely that they will accept credit. Home centers, department stores, brand stores, some higher end hair salons, etc often accept them, but smaller boutiques, restaurants, bars, etc often do not.
Also, even when I go to Tokyo, I still like to carry cash even though credit cards are more readily usable there. Why do I? Because for every business I go to, even in Tokyo, that accepts credit, I end up walking into another that still doesn’t. Rather than worrying about who will accept credit and who won’t, it is simply easier (for me, at least) to carry cash.
And, Sublight, I have had a couple friends get themselves in semi-serious credit problems because of revolving credit, so I can only assume it is allowed here. But I may be wrong, myself.
I think it is also worth pointing out that, for many people, card loans seem more popular than credit cards as a source of credit for purchases. I’ve never used one, so I cannot go into the particulars, but basically, with a card loan, a bank extends you a line of credit and gives you a card that is similar to an ATM card. You can use this card to withdraw cash on credit from an ATM, rather than from a bank account, and use that cash to make purchases, much like a cash advance on a credit card.
When I studied in Tokyo, I used my credit card fairly often to make purchases and it was certainly convenient. But having moved out of the Tokyo region, I’ve become a lot more accustomed to carrying cash and I haven’t used my credit card since. But, like any country, Japan is not one small entity and each region is different. So OMMV depending on where in Japan one might live or visit.