Real-world objects contain state and behavior.
A software object's state is stored in fields.
1.A software object's behavior is exposed through methods.
2.Hiding internal data from the outside world, and accessing it only through publicly exposed methods is known as data encapsulation.
3.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.