核心技术出错了

import java.util.*;
public class EmployeeTest { /**
 * @param args
 */
public static void main(String[] args) {
Employee[] staff = new Employee[3];

staff[0] = new Employee("K",75000,1987,12,15);
staff[1] = new Employee("L",50000,1989,10,1);
staff[2] = new Employee("P",40000,1990,3,15);

for(Employee e:staff)
e.raiseSalary(5);

for(Employee e:staff)
System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay=" + e.getHireDay());
// TODO Auto-generated method stub }}class Employee{
public Employee(String n,double s, int year, int month,int day){
name = n;
salary = s;

GregorianCalendar calendar = new GregorianCalendar(year,month-1,day);
hireDay = Calendar.getTime();
}

public String getName(){
return name;
}

public double getSalary()
{
return salary;
}
public Date getHireDay(){
return hireDay;
}
public void raiseSalary(double byPercent){
double raise = salary * byPercent/100;
salary += raise;

}

private String name;
private double salary;
private Date hireDay;

}
java核心技术上的一段代码，编译起来竟然报错，还请大虾们指点
 无法从静态上下文中引用非静态 方法 getTime()
       hireDay = Calendar.getTime()