What is the essence of object-oriented inheritance in Java?

1.What is inheritance?

(1) Used to improve code reusability

(2) Encapsulate the same functional module into a method and call the method when needed to achieve the purpose of code reuse

(3) Extract the same class content from multiple classes through inheritance and turn it into a new class, allowing other classes to have a relationship with the current new class to achieve the purpose of code reusability. Note: Java is a single Inheritance is different from c. C can have multiple inheritance.

2. Inherited format

Keyword extends

3. Inherited features

*The subclass has the non-private attributes and methods of the parent class.

*Subclasses can have their own properties and methods, that is, subclasses can extend parent classes.

*Subclasses can implement the methods of the parent class in their own way.

*Java inheritance is single inheritance, but multiple inheritance is possible. Single inheritance means that a subclass can only inherit one parent class. Multiple inheritance means that, for example, class B inherits class A, and class C inherits class B, so According to the relationship, class B is the parent class of class C, and class A is the parent class of class B. This is a feature that distinguishes Java inheritance from C inheritance.

*Improved the coupling between classes (disadvantages of inheritance, high coupling will cause the closer the connection between codes, the worse the code independence)

4. A class inherits from its parent class. When we create a subclass object, what happens in memory? ?

As shown below:

Picture source Han Shunping b station link

It can be seen that the subclass object has all the attributes of the parent class, but if we access Who will name visit?

5. Permission modifier

Note: Applicable to both properties and methods. Default means nothing needs to be written in front of the return type (data type).

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