Access Characteristics of Constructor under Inheritance Relationship

Table of Contents​​​​​​​

Foreword

I. super keyword

two, Access Features

Three, this keyword

Summary

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Foreword

First of all, let's understand the basic concept of inheritance. Inheritance describes the relationship between things. Through inheritance, a relationship system can be formed between various things. In JAVA, class inheritance refers to aOn the basis of the existing class, build a new bit, the constructed mind is called the subclass, the existing class is called the parent class, and the subclass inherits the properties and methods of the parent class, so that the subclass object has the characteristics andBehavior.The format is as follows:

class parent class{....}class subclass extends superclass{....}

one, super keyword

When the subclass overrides the method of the parent class and the subclass object will not be able to access the overridden method of the parent class, in order to solve this problem, the super keyword provided by JAVA, the super keyword can call the parent class in this classThe common attribute method and construction method of , the specific usage of the super keyword is explained in detail below:

(1) Use the super keyword to access the member variables and methods of the parent class

super.member variablessuper.member method(parameter 1, parameter 2...)

(2) Use the super keyword to access the constructor specified in the parent class

super(parameter1, parameter2..)

II. Access features

(1) In the constructor of the subclass, if a super(); is not displayed, one will be given by default, and if one is displayed, it will not be given.

Pay attention to the code of the above two pictures. In the second picture, we wrote a super(), which is the same as the first one without writing. It can be proved that if there is no writing displayed, thenOne will be given by default. If one is displayed, it will not be given again.

(2) super (parameter), must be the first statement, otherwise an error will be reported. When creating a subclass object, the subclass will definitely call a constructor of the parent class. If there are no parameters, the default call will be no parameters.Constructor, if there are parameters, call the parameterized constructor.

Three, this keyword

Common usage:

this.member variables of this class

this.member method of this class

this(parameter)

(1) Access the attribute in this class, if this class does not have this attribute, look it up from the parent class.

(2) Access the method in this class, if this class does not have this method, look it up from the parent class.

(3) must be written in the first line of the constructor (so super() this() cannot exist at the same time).

(4) Only other constructors of this class can be called, not themselves (that is, they cannot be called recursively, and the constructor itself cannot be called directly or indirectly through this in a constructor).

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Summary

The above is my access to the construction method under the inheritance relationship. It mainly introduces the two keywords super and this, as well as some special usage methods and precautions. There are still many shortcomings in the article, I hope you will point out.