我们来看以下这段程序:
public class Employee {
private String name;
private double salary;
private LocalDate hireDay;
public Employee(String name, double salary, int year, int month, int day) {
this.name = name;
this.salary = salary;
hireDay = LocalDate.of(year, month, day);
}
public String getName() {
return name;
}
public double getSalary() {
return salary;
}
public LocalDate getHireDay() {
return hireDay;
}
public void raiseSalary(double byPercent) {
double raise = this.salary * byPercent / 100;
salary += raise;
}
}
public class Manager extends Employee{
private double bonus;
public Manager(String name, double salary, int year, int month, int day) {
super(name, salary, year, month, day);
}
@Override
public double getSalary() {
return super.getSalary() + bonus;
}
public void setBonus(double bonus) {
this.bonus = bonus;
}
}
public class ManagerTest {
public static void main(String[] args) {
Manager boss = new Manager("Jackey Ma", 80000, 1975, 12, 15);
boss.setBonus(10000);
Employee[] staffs = new Employee[3];
staffs[0] = boss;
staffs[1] = new Employee("Pony Ma", 40000,1974,1,15);
staffs[2] = new Employee("Lei Jun",35000,1973,11,15);
for (Employee staff : staffs) {
System.out.println("名字 = " + staff.getName() + ", 薪水 = " + staff.getSalary());
}
}
}
程序运行后打印输出结果为:
名字 = Jackey Ma, 薪水 = 90000.0
名字 = Pony Ma, 薪水 = 40000.0
名字 = Lei Jun, 薪水 = 35000.0
我们借助这个例子来学习多态,所谓的多态就是一个对象变量(比如上文中的staff变量)可以指示多种实际类型的现象(比如staff既可以引用Employee对象,也可以引用它的子类Master对象)被称为多态。在运行时候能够自动地选择调用哪个方法的现象被称为动态绑定(比如,staffs[0]调用的是Master类中的 getSalary()
方法,而staffs[1]和staffs[2]调用的是Employee类的 getSalary()
方法)。