JAVA class and object ------ inheritance, java ------ inheritance

Source: Internet
Author: User

JAVA class and object ------ inheritance, java ------ inheritance

Understanding: inheritance can be understood as an object's process of obtaining attributes. If Class A is the parent class of Class B, and Class B is the parent class of class C, we also say that C is A subclass of Class A, and class C is inherited from Class. In java, class inheritance is a single inheritance, that is, a subclass can only have one parent class.

Keywords: extends and implements.

The use of these two keywords determines whether an object is a IS-A (a) relationship with another object.

Example:

// A.javapublic class A {    private int i;    protected int j;     public void func() {     }} // B.javapublic class B extends A {}

Note: In the preceding example, B is inherited by A, and B is A subclass of. As A subclass, B's instance has all the member variables of A, but has no access permission to private member B, which guarantees the encapsulation of.

 

IS-A relationships: one object is another object category! We can determine the Mammal IS-A Animal by using the instanceof operator.

class Animal{}class Dog extends Animal{}class Cat extends Animal{}class Pig extends Animal{}public class AnimalTest{    public static void main(String args[]){        Dog dog=new Dog();        Cat cat=new Cat();        Pig pig=new Pig();        System.out.println(dog instanceof Animal);        System.out.println(cat instanceof Animal);        System.out.println(pig instanceof Animal);    }}

 

Let's take a look.ImplementsHow the keyword is used to represent the IS-A relationship.

ImplementsKeywords cannot be used in this case when the class inheritance interface is used.Extends.

interface Animal{}class Mammal implements Animal{}class Dog implements Animal{}public class AnimalTestTwo {   public static void main(String args[]){      Mammal m = new Mammal();      Dog d = new Dog();      System.out.println(m instanceof Animal);      System.out.println(d instanceof Animal);   }} 

 

 

Java only supports single inheritance (inheriting basic classes and abstract classes), but we can use interfaces (implementing multiple inheritance interfaces). The script structure is as follows:

Public class Apple extends Fruit implements Fruit1, Fruit2 {}
Generally, we use the extends keyword to inherit basic classes and abstract classes, and use the implements keyword to inherit interface classes.

Related Article

Contact Us

The content source of this page is from Internet, which doesn't represent Alibaba Cloud's opinion; products and services mentioned on that page don't have any relationship with Alibaba Cloud. If the content of the page makes you feel confusing, please write us an email, we will handle the problem within 5 days after receiving your email.

If you find any instances of plagiarism from the community, please send an email to: info-contact@alibabacloud.com and provide relevant evidence. A staff member will contact you within 5 working days.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

  • Sales Support

    1 on 1 presale consultation

  • After-Sales Support

    24/7 Technical Support 6 Free Tickets per Quarter Faster Response

  • Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.