Japan is known for its cleanliness.
Japanese take pride in keeping their locality clean and tidy. In fact, many Japanese feel it is a fundamental duty of every citizen.
Japanese are taught to keep their surroundings clean from a very young age. In schools, students are often encouraged to clean up the corridors which would otherwise, be done by a janitor. This creates a good habit for young children and make them self-conscious growing up. I have worked in several countries (USA, Austria, England, Taiwan and Japan) and although, all of those countries are neat and clean I felt the sense of responsibility in Japan was higher for an average citizen when it comes to aesthetics of public places. I come from a country which has a huge garbage problem and I believe the densely populated public places of Japan are clean because of the mentality of their citizens.
Japanese society is based on discipline and self-restraint.
People not only keep their houses/shops clean but they also make sure the street (extending beyond their immediate surroundings) is clean.
During my stay in Japan I used the train to commute to office daily. As, I rushed on my way to office daily, I used to find a man wearing a suit cleaning the footpath in front of the Meitetsu ticket counter. This ticket counter was out on the street and not inside the railway station. I was amazed that there were such good uniforms for cleaners in Meitetsu Rail Company. But, I was wrong. I found out later that he was not one of the cleaning staff but was in fact the ticket collector for that station. He daily cleaned the space in front of his counter before his job started at 9 AM. I was humbled by the experience and wished the same attitude could prevail in my country.
I have observed many Japanese people stroll out on to the streets with an empty garbage bag to pick out the leaves that fall on the footpath during fall season. This act of voluntary cleaning up of streets is to show gratitude towards their community and country. One would also come across many volunteers at festivals who help in collecting trash. Internationally, the Japanese culture of cleanliness came into limelight during 2014 Football world cup matches in Brazil when news of Japanese fans voluntarily clearing the trash in the stadium were published.
People seldom litter in the train stations or at huge public gatherings such as festivals and concerts. It was interesting for me to find out during the many summer festivals I have attended there were no garbage bins for people to throw away garbage. Although, I found it quite uncomfortable to carry the garbage back home from the festival I was amazed to see there was hardly any garbage in the place where the festivals took place. Yes, people have to carry their garbage back home from festivals in Japan (even though you buy your food at the festival)! I guess this system would only work in Japan as only Japanese are trained to follow such rules.
I did not find any Japanese person complaining about the lack of trash bins. Here is some advice for foreigners who go to public gatherings. Unless, you plan on carrying garbage back home, dump your garbage at the same place where you bought the food. One can also use the trash cans at convenience stores as they accept garbage from everybody.
Not just the clean streets but many Japanese houses and stores are well decorated at their entrance with small plants in pots. They are usually arranged in an attractive manner to welcome their guests. One truly feels welcome in such nice cozy environment.