What is the premise of polymorphism in java?

Three conditions are needed to realize polymorphism in java:

1, inheritance relation is required.

2. Need a rewriting method.

3. The reference of the parent class needs to point to the subclass object.

Java learning recommends that you come to Beijing to attend school. Strong teachers bring you a different learning experience. I hope it will be helpful for you to share the route of java learning:

First, the basic stage of JavaSE

Object-oriented programming (basic)

Object-oriented programming (advanced)

Abnormal mechanism

Java public class

Data structure and algorithm

Collection (container)

IO stream

Multithread operation

Network programming

Group promotion training

Multi-thread lifting training

Second, the database stage.

MySQL foundation

MySQL query statement

Database object

JDBC

Reflection and interpretation

Database modeling and UML modeling

Design pattern

Third, the WEB front end.

Java Script language

jQuery

bootstrap program

A video editing software

Four. JavaEE stage (core stage)

HTTP/Tomcat

MVC architecture

Small application program

JSP

EL+JSTL+ filter+listener

Ajax and JSON

Pagination and file upload/download

Verb (abbreviation of verb) JavaEE stage (high-level framework)

Spring 5.2.2

Spring MVC 5.2.2

RBAC

EasyUI 1.7.0

Payment/SMS verification

Frame reinforcement of intransitive verbs

Linux - CentOS 8

expert

recall

quartz

Spring Boot 2.2.2

Shiro

fashionable

Git/GitEE

Mibatis

Seven, distributed architecture

Zoo keeper

Remote position control

Bo Du

Radice

Thor

Rabbit q

FastDFS

Nginx

Spring safety

Spring meeting

Maybatis generator

My cat

Eight, micro service stage

Elastic search

MongoDB

Chun Yun Wang Fei Eureka

Chunyun net flying ribbon

Spring clouds open and pretend

Chunyunwang Feihai Strix

Spring cloud configuration

Chunyun gateway

roustabout

K8S