import java.util.*;
public class EmployeeTest
{
    public static void main(String[] args)
    {
        Employee[] staff = new Employee[3];
        staff[0] = new Employee("张三",75000,1987,12,15){};
        staff[1] = new Employee("李四",50000,1989,10,1){};
        staff[2] = new Employee("王五",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());
    }
}
class Employee
{
    private String name;
    private double salary;
    private Date hireDay;
    public Employee(String n,double s,int year,int month,int day)
    {
        String name = n;
        double 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;
    }
   
   
}

Employee类中的构造函数有问题
String name = n;
double salary = s;
这两句话重新定义了String变量 name, double变量 salary，将n, s的值赋给name,salary，而方法中定义的 String name, double salary，在方法体执行完成后，会被垃圾收集器收回内存,里面的值也就没了，
主要是你没有把 方法参数n, s的值赋给类的成员变量name，salary,
上面两句话改为：
 this.name = n;
 this.salary = s;
就能正常运行了

谢谢了  ，你说的很对