What is class?

A class is a blueprint or prototype from which objects are created. In the real world, you'll often find many individual objects all of the same kind.
The following Bicycle class is one possible implementation of a bicycle:

class Bicycle {

      int cadence = 0;
      int speed = 0;
      int gear = 1;

      void changeCadence(int newValue) {
           cadence = newValue;
      }

      void changeGear(int newValue) {
           gear = newValue;
      }

      void speedUp(int increment) {
           speed = speed + increment;  
      }

      void applyBrakes(int decrement) {
           speed = speed - decrement;
      }

      void printStates() {
           System.out.println("cadence:"+cadence+" speed:"+speed+" gear:"+gear);
      }
}