Polymorphic (Java)

One, polymorphic

1, what is polymorphic?

Parsing: Different objects respond differently to the same operation

Features that have the ability to express multiple forms

2. Advantages of using polymorphism

Parsing: In order to achieve unified invocation

A small example:< the parent class type as a parameter >

Parent class (Pet) subclass (Gog,penguin) master Human (master) test Class (test)

Pet

Public abstract class Pet {public    abstract void Eat ();}

Dog

   public class Dog extends pet{    @Override public    void Eat () {        System.out.println ("Enough to eat Bones");            }

Penguin

   public class Penguin extends Pet {    @Override public    void Eat () {        System.out.println ("Penguin Eats Fish");            }

Master

public class Master {    //parent class type as parameter public void feed (Pet pet) {    pet.eat ();    }}

Test

    public static void Main (string[] args) {        Master master=new master ();                Pet pet=new Dog ();                Master.feed (PET);    }

Transformation of subclasses to parent class (upward transformation)

Rules:

① a reference to a parent class to a subclass object, which becomes an upward transformation, automatic type conversion

② a method that is called by a parent class reference variable is a child class that overrides or inherits a method of the parent class, not the parent class's method

③ a method that is unique to a subclass cannot be called through a parent class reference variable

Third, two ways to implement and use polymorphism in Java

① using a parent class as a method parameter

② using the parent class as a method return value

Iv. conversion of parent class to subclass (downward transition)

Assigns a reference to a subclass object to a parent class reference, called a downward transformation. Forced type conversions are required at this time

Five, instanceof operators

Grammar:

Object instanceof class or interface

This operator is used to determine whether an object belongs to a class or implements an interface with the result of true or false

Note:

① when using the instanceof operator, the object must be of the same type as the class or interface specified by the second parameter of Instanceof, or a compilation error will occur

②instanceof commonly used in conjunction with forced type conversions

Polymorphic (Java)