继承与static-阅读EmployeeTest.java代码

尝试阅读EmployeeTest.java代码。

import java.util.*;

/**
 * This program tests the Employee class.
 * @version 1.11 2004-02-19
 * @author Cay Horstmann
 */
public class EmployeeTest
{
   public static void main(String[] args)
   {
      // fill the staff array with three Employee objects
      Employee[] staff = new Employee[3];

      staff[0] = new Employee("Carl Cracker", 75000, 1987, 12, 15);
      staff[1] = new Employee("Harry Hacker", 50000, 1989, 10, 1);
      staff[2] = new Employee("Tony Tester", 40000, 1990, 3, 15);

      // raise everyone's salary by 5%
      for (Employee e : staff)
         e.raiseSalary(5);

      // print out information about all Employee objects
      for (Employee e : staff)
         System.out.println("name=" + e.getName() + ",salary=" + e.getSalary() + ",hireDay="
               + e.getHireDay());
   }
}

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);
      // GregorianCalendar uses 0 for January
      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;
}

并回答:

1. raiseSalary方法有什么用?

• 体现加薪的功能，先计算增加部分=原来薪水*percent，再加上原有薪水，即最终薪水

2. 代码中3个Employee对象调用raiseSalary方法所执行的代码一样吗?返回结果一样吗?为什么?

• 调用raiseSalary方法所执行代码是一样的，只是返回结果有所不同，虽然薪水提高5%，但是3个Employee的薪水不一致，所以加薪后的工资也不一致

3. 能不能将raiseSalary定义为static?结合该例子,你觉得一般来说什么样的方法应该声明为static?

• 不能，因为静态方法不能直接调用非静态成员和方法
• 当需要初始化或不用生成类的实例就可以直接调用时，可以使用static