There are three main features of Java object-oriented design: encapsulation, inheritance and polymorphism

There are three main features of Java object-oriented design: encapsulation, inheritance and polymorphism

a package of

1.1 Concept: It is to hide some of the class's sensitive information in the class section of the class, not directly accessible to the outside world, but can be accessed indirectly through the Getter/setter method.

1.2 Purpose: We can and may, in the method, add their own restrictions to ensure the validity of the data, in a way, the package also improves the robustness of the code, security.

1.3 Implementation steps: All member variables are privatized, format: Private data type variable name, provides access to member variable Getter/setter method.

Ii. inheritance

2.1 Concept: Subclasses accept all public, protected member variables and member methods of the parent class in a way.

2.2 Purpose: Enhance the reusability of code and improve the quality of code.

2.3 Implementation steps: Using extends keyword, identity subclass inherits parent class, format: public class subclass name extends parent class name

2.4 Note: The ⑴ subclass can override the method of the parent class on the basis of inheriting the parent method, and in the concrete execution is the method of executing the subclass;

⑵ subclasses can define their own properties, methods, which is a manifestation of code extensibility;

All classes in ⑶java, if no defined definition inherits from, the default is inherited from Object;

⑷ (special note) in Java, each class can inherit only one class ———— Java's single-inheritance mechanism.

Tri-Polymorphism

3.1 Concept: In the course of operation, the same type behaves differently under different conditions, and the representation of this indeterminate state can be called polymorphism.

3.2 Category: Ⅰ. Design-time polymorphism: Polymorphism of method overloading implementations

⑴ method overloads ————— All methods defined are declared in the "same class";

The implementation of the ⑵ method overload ———— the same method name (different parameters) {}, for example: public void person () {...}

and public void person (String name) {...}

Ⅱ. Run-Time polymorphism: Method "Override" the implementation of polymorphism

The ⑴ method overrides/Overrides ———— defined methods are definitely methods that override the parent class in a subclass, and the method appears in two classes.

The implementation of the ⑵ method overrides ———— subclass inherits the parent class and then re-sorts the implementation of the clothes class method in the subclass.

Example: Parent public class pet{}

Subclass public class cat{} subclass inherit parent Cat extends Pet

Pet cat = new Cat (); The reference to the parent class points to the object of the subclass, which represents the run-time polymorphism.

There are three main features of Java object-oriented design: encapsulation, inheritance and polymorphism