在子类中调用方法

Question

我有一个超类 (Employee)，它实现了一个只包含 1 个方法的接口，如下所示。

public interface Payable 
{    
   double getPaymentAmount(); // calculate payment; no implementation
}

我有许多继承自 Employee 的子类（例如 SalariedEmployee、HourlyEmployee、CommissionEmployee），每个子类都包含一个方法 Earnings。

我被要求“可以修改 Employee 类以实现接口 Payable 并声明方法 getPaymentAmount 以调用方法 Earnings。然后方法 getPaymentAmount 将由 Employee 层次结构中的子类继承。当为特定子类对象调用 getPaymentAmount 时，它多态地为该子类调用适当的收益方法”。

如何在Employee类方法getPaymentAmount中调用相关的收入方法而不用编辑子类？

我是 Java 的新手。

Employee类的相关部分如下：

public abstract class Employee implements Payable
{
   private String firstName;
   private String lastName;
   private String socialSecurityNumber;

   // three-argument constructor
   public Employee( String first, String last, String ssn )
   {
      firstName = first;
      lastName = last;
      socialSecurityNumber = ssn;
   } // end three-argument Employee constructor
    //getters, settters, toString override etc have been deleted. 
   public double getPaymentAmount()
   {
       ????    //This is what I need help with.        
   }

} // end abstract class Employee

并以子类为例：

public class SalariedEmployee extends Employee
{

    private double weeklySalary;

    // four-argument constructor
    public SalariedEmployee(String first, String last, String ssn, double salary)
    {
        super(first, last, ssn); // pass to Employee constructor
        setWeeklySalary(salary); // validate and store salary
    } // end four-argument SalariedEmployee constructor

    @Override
    public double earnings()
    {
        return getWeeklySalary();
    } // end method earnings

} // end class SalariedEmployee

Answer 1

也许这就是您要找的东西？为了实现多态行为，让你的各种 Employee 类对earnings() / getPaymentAmount() 有不同的实现。这样做会导致方法覆盖其超类，从而实现多态性。

class Employee implements Payable
{
    double getPaymentAmount(){
        return earnings();
    }
    double earnings(){
        //Your other implementations
        return xxx;
    }   
}

class SalariedEmployee extends Employee
{
    double getPaymentAmount(){
        return earnings();
    }
    double earnings(){
        //Different implementation for different employee tpye
        return xxx;
    } 
}

“如何调用Employee类方法getPaymentAmount中的收入相关方法？”

没有必要担心这一点。 Java 会为您解决这个问题。这就是多态性的基础。根据对象的类，它们会调用各自的方法。

Answer 2

我认为您正在寻找的是这样的：

abstract class Employee implements Payable
{
    double getPaymentAmount(){
        return earnings();
    }

    abstract double earnings();
}

class SalariedEmployee extends Employee
{

    double earnings(){
        //Different implementation for different employee tpye
        return xxx;
    } 
}

由于您声明了一个名为earnings 的abstract 方法，因此abstract class 的其他方法可以调用该方法，因为它们知道Employee 的任何实例化实例都必须具有实现的earnings 方法。

Answer 3

Employee.java
=======================================================================
interface Payable
{
    double getPaymentAmount(); // calculate payment; no implementation
}

public abstract class Employee implements Payable{
    public double getPaymentAmount()
    {
        return 0.0;
    }

    public void printSalary()
    {

    }
}


Teacher.java
=======================================================================
public class Teachers extends Employee {
    public double getPaymentAmount()
    {
        return 5;
    }

    public void printSalary()
    {
        System.out.println("Teachers current salary is: " + getPaymentAmount());
    }

}

SoftwareEngineer.java
=======================================================================
public class SoftwareEngineer extends Employee {
    public double getPaymentAmount()
    {
        return 500;
    }

    public void printSalary()
    {
        System.out.println("Software Engineers current salary is: " + getPaymentAmount());
    }

}

TestEmployee.java
=======================================================================
public class TestEmployee {
    public static void main(String s[])
    {
        Employee e = new Teachers();
        e.printSalary();

        Employee e1 = new SoftwareEngineer();
        e1.printSalary();
    }
}