- Real-world objects contain state and behavior.
- A software object's state is stored in fields.
- A software object's behavior is exposed through methods.
- Hiding internal data from the outside world, and accessing it only through publicly exposed methods is known as data encapsulation.
- A blueprint for a software object is called a class.
- Common behavior can be defined in a superclass and inherited into a subclass using the extends keyword.
- A collection of methods with no implementation is called an interface.
- A namespace that organizes classes and interfaces by functionality is called a package.
- The term API stands for Application Programming Interface.