1. Abstraction: it is the process of summarizing the common characteristics of a class of objects to construct a class. It includes data abstraction and behavior abstraction, that is, abstract classes and abstract methods. Abstract only focuses on the properties and methods of objects, not on what functions these methods implement.
2. Encapsulation: Bind the properties of an object to the methods that manipulate the properties. To use these properties and methods, you can only call the defined interface.
Inheritance: The process of creating a new class by inheriting information from an existing class. Classes that provide inherited information are called superclasses (superclasses, base classes), and classes that receive inherited information are called subclasses (derived classes). Java inheritance can only be single inheritance. A class cannot inherit multiple classes. A class can be inherited by multiple classes.
4. Polymorphism: It means that objects of different subtypes can make different responses to the same message. Parent p = new Child(); Parent p = new Child(); There are three ways to implement polymorphism: abstract classes and methods, interfaces, and overrides.
