在C ++中实现简单的Java程序（抽象类）

Question

Java (Works)

Abstract class Personnell with subclasses of Manager and Worker. getAnnualIncome() is the abstract function.

Personnell employee[] = 
{
    new Manager("Thomas", "Nasa", 1337, 250000),
    new Worker("Simon", "Netto", 1336, 6.98, 36)
};
System.out.println("Name\t\tAnnual Income");
for (int i = 0; i < employee.length; i++)
{
System.out.printf(employee[i].getName() + "\t\t£%.2f%n", employee[i].getAnnualIncome());
}

C++ (Doesnt work)

Personnell employee[] = 
{
    Manager ("Tom", "Ableton", 1234, 400000),
    Worker ("Simon","QuickiMart", 666, 40, 3.50)
};

cout << "Name\t\tJob\t\tAnnual Income"<< endl<<endl;
for (int i = 0; i < 3; i++)
{
    cout << employee[i].getName() << "\t\t"<< employee[i].getDept()<<"\t\t"<< employee[0].getAnnualIncome() << endl;
}

Error: array of Abstract class "Personnell" is not allowed: function "Personnell::getAnnualIncome" is a pure virtual function

Tried a few different things to do with pointers but I still need to get my head around them. Thanks, Tom

Edit (adding definitions and declarations) Personnell has

virtual double getAnnualIncome()=0;

Manager has

double getAnnualIncome(); //declaration
double Manager::getAnnualIncome() //definition
{

return this->salary_;
}

Worker has

double getAnnualIncome(); //declaration
double Worker::getAnnualIncome() //definition
{
return (this->hourlyRate_ * this->hoursPerWeek_)*52;
}

doing what ajb said, the output is:

Name Job Annual Income

Tom Ableton 400000

Simon QuickiMart 400000 // Should be 7280

Answer 1

In C++, when you create an array with the type of the base class object, something called object slicing happens: ie when you declare an array of an abstract class and you put child classes in it, only the abstract parts (ie pure virtuals) are stored. And as you saw, you cannot call pure virtual functions because the objects in your employee array are sliced objects.

Answer 2

You can't have an array of Personnell objects, because Personnell is an abstract type, and the compiler won't know how big to make each array element. So you need to use pointers. (It works in Java because, in effect, Java automatically uses pointers.)

Change the employee definition to

Personnell *employee[] = 
{
    new Manager ("Tom", "Ableton", 1234, 400000),
    new Worker ("Simon","QuickiMart", 666, 40, 3.50)
};

and instead of

cout << employee[i].getName() << "\t\t"<< employee[i].getDept()<<"\t\t"<< employee[0].getAnnualIncome() << endl;

use -> since employee[i] is now a pointer:

cout << employee[i]->getName() << "\t\t"<< employee[i]->getDept()<<"\t\t"<< employee[i]->getAnnualIncome() << endl;

(The last employee[0] is a typo and should be changed to employee[i] ; also, for (int i = 0; i < 3; i++) looks like a typo since there are only two elements in the array.)