What are the three major characteristics of java object-oriented

Java's three major object-oriented features: 1. Encapsulation, which aims to enhance data security and simplify programming; 2. Inheritance, which refers to extracting multiple identical properties and methods and creating a new parent class , the purpose is code reuse; 3. Polymorphism, the purpose is to increase the flexibility of the code.

The operating environment of this tutorial: windows7 system, java8 version, DELL G3 computer.

Three major characteristics of Java object-oriented

1. Encapsulation

Encapsulation It refers to the privatization of properties

• Provide setter and getter methods to access properties as needed
• Hide specific properties and implementation details, and only open the interface to the outside world
• In the control program Attribute access level

Purpose: Enhance data security, prevent other users from accessing and modifying data at will, simplify programming, users do not need to care about specific implementation details, but just pass The external interface can access the members of the class

2. Inheritance (Extend)

Inheritance refers to extracting multiple identical properties and methods Come out and create a new parent class

• A class in Java can only inherit one parent class, and can only inherit access permissions and non-private properties and methods
• Subclasses can override the parent class In the method, name the attribute with the same name as in the parent class

Purpose: Code reuse

3. Polymorphism

Polymorphism (Polymiorph) can be divided into two types: design-time polymorphism and run-time polymorphism

Design (compile)-time polymorphism: Overload , means that Java allows the same method name but different parameters (the return value can be the same or different). One or more functions with the same name are allowed to exist in the same class, as long as the parameter type or number of parameters are different

Runtime polymorphism: That is, override must be in the inheritance system. The subclass overrides the parent class method. The JVM runtime determines which method to call based on the type of the method being called.

Purpose: Increase the flexibility of the code

Summary:

1. Inheritance should be minimized in java relationship to reduce coupling

2. When using polymorphism, when the parent class calls a method, it will first call the method of the subclass. If the subclass does not override the method of the parent class, then the method of the parent class will be called. Method

3. Java access control character scope table:

##This class This class Package Subclass External package ##public protected default private ##✓: Can be accessed X: Inaccessible

✓	✓	✓	✓
✓	✓	✓	X
✓	✓	X	X
✓	X	X	X

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