java casual notes three polymorphisms

Polymorphism:

---Multiple forms of an object

Essence: The reference of the parent class points to the child class object

---Prerequisite: There must be inheritance or implementation

class Animal{}

class Dog extends Animal{}

main{

Dog d = new Dog(); //Original state

Animal dog = new Dog(); //Polymorphic

}

Note: Created through polymorphic form The object can only access the member methods common to the child and parent classes. The result of the operation is that the member methods unique to the subclass cannot be used.

Virtual method call:

The parent class object calls the subclass-specific method

Student S = new Student("张三",100);

Person p = new Student("李思",200);

System.out.println(S.say());

System.out.println(p.say());

Polymorphic array - In an array of reference types, use polymorphic form to store objects .

eg:Person[] person = {new Person("张三", 32),

new Student("李四", 21, 120, 90.0),

new Student("王五", 22, 119, 91.5),

new Teacher("Teacher Liu", 35, 10, "Java EE"),

new Teacher("Teacher Zhang", 11)};

Polymorphic parameters - method parameter list The reference type parameter in

instanceof operator - determines whether an object is of a specified type (form)

Forced type conversion - converts an object from one reference form to another reference form

Object association:

an object Another object is used in

One-to-one, one-to-many, many-to-one

class test4 {
public static void main(String[] args){
 
Person p = new Person("王五",50);
method(p);
Student S = new Student("张三",100);
method(S);
Person p1 = new Student("赵四",100);
method(p1);
}
 
public static void method(Person p){
if (p instanceof Student){
System.out.println("教师");
Student s = (Student)p;
System.out.println("本态方法调用："+p.say());
}else{
System.out.println("人");
}
 
System.out.println(p.say());
}
}
 
class Person{
private String name;
private int age;
 
public Person(){}
 
public Person(String name,int age){
this.name = name;
this.age = age;
}
 
public String getName(){
return name;
}
 
public String say(){
return "姓名:"+name+"年龄:"+age;
}
}
 
class Student extends Person{
private int id;
private double score;
 
public Student(String name,int id){
this(name,20,id,98.5);
}
 
public Student(String name,int age,int id,double score){
super(name,age);
this.id = id;
this.score = score;
}
 
public double getId(){
return id;
}
 
public String say(){
return super.say()+"学号:"+id+"分数:"+score;
}
}