That is because this particular class secretly calls another constructor, a constructor hidden in the Object class. The Object class is a class of the general Java environment, that is always there, but mainly hidden to us. Remember, a constructor is always needed, one that we'll make ourselves, or a default constructor by the system. The Mouse we're building will have a constructor would create instances like the Case, Buttons, Cable and the RecognizeMovement, and tie them together to form the mouse object MyMouse. It will certainly initiate most of these instances to neutral states.
Every object has some actions to perform.
Sooner or later we will ask it to do something. The Printer instance will get a print work to do, the buttonPressed will cause a signal sent to the computer when it's pressed down, and later when it's released. Most instances will perform a task in due time. The part of the code written to stir up some action is called method . Other programming languages call it function, procedure, etc.