无涯教程-Java - 多态多态性是对象表现为多种形式的能力。OOP中多态性最常见的用法是使用父类引用子类对象。如

多态性是对象表现为多种形式的能力。OOP中多态性最常见的用法是使用父类引用子类对象。

如果引用变量未声明为final，则可以将其重新分配给其他对象。引用变量的类型将确定它可以在对象上调用的方法。

让无涯教程看看一个例子。

public interface Vegetarian{}
public class Animal{}
public class Deer extends Animal implements Vegetarian{}

现在，Deer类被认为是多态的，因为它具有多重继承，以下声明是合法的-

Deer d = new Deer();
Animal a = d;
Vegetarian v = d;
Object o = d;

所有引用变量d，a，v，o都引用堆中的相同Deer对象。

已经讨论了方法重写，其中子类可以重写其父类中的方法。被重写的方法本质上隐藏在父类中，除非子类在重写方法中使用super关键字，否则不会调用该方法。

/* File name : Employee.java */
public class Employee {
   private String name;
   private String address;
   private int number;
public Employee(String name, String address, int number) {
System.out.println("Constructing an Employee");
this.name = name;
this.address = address;
this.number = number;
}
public void mailCheck() {
System.out.println("Mailing a check to " + this.name + " " + this.address);
}
public String toString() {
return name + " " + address + " " + number;
}
public String getName() {
return name;
}
public String getAddress() {
return address;
}
public void setAddress(String newAddress) {
address = newAddress;
}
public int getNumber() {
return number;
}
}

现在假设无涯教程扩展Employee类，如下所示-

/* File name : Salary.java */
public class Salary extends Employee {
   private double salary; //年薪
public Salary(String name, String address, int number, double salary) {
super(name, address, number);
setSalary(salary);
}
public void mailCheck() {
System.out.println("Within mailCheck of Salary class ");
System.out.println("Mailing check to " + getName()
+ " with salary " + salary);
}
public double getSalary() {
return salary;
}
public void setSalary(double newSalary) {
if(newSalary >= 0.0) {
salary = newSalary;
}
}
public double computePay() {
System.out.println("Computing salary pay for " + getName());
return salary/52;
}
}

现在，您仔细研究以下程序并尝试确定其输出-

/* File name : VirtualDemo.java */
public class VirtualDemo {
public static void main(String [] args) {
Salary s = new Salary("Mohd Mohtashim", "Ambehta, UP", 3, 3600.00);
Employee e = new Salary("John Adams", "Boston, MA", 2, 2400.00);
System.out.println("Call mailCheck using Salary reference --");

s.mailCheck();
System.out.println("\n Call mailCheck using Employee reference--");
e.mailCheck();
}
}

这将产生以下输出-

Constructing an Employee
Constructing an Employee
Call mailCheck using Salary reference --
Within mailCheck of Salary class
Mailing check to Mohd Mohtashim with salary 3600.0
Call mailCheck using Employee reference--
Within mailCheck of Salary class
Mailing check to John Adams with salary 2400.0

这种行为称为虚方法调用，而这些方法称为虚方法。

无涯教程-Java - 多态

参考链接