Thread: abstract class & 'covariant' return type?

Hi Forum,

I have written an abstract class called 'Field', which within has an abstract method called 'getValue()'. So, so far I have:-

public abstract class Field
{
// instance variables
private double x;
private double y;


public Field(double x)
{
this.x = x;
}

public Field(double x, double y)
{
this.x = x;
this.y = y;
}


abstract double getValue();

}


Now, I have two subclasses of Field, called 'Real' and 'Complex', which both have concrete implementations of the method 'getValue()'. So, they both look like:-


public class Real extends Field
{
// instance variables
private double x;

public Real(double a)
{
super(a);
}


public double getValue()
{
return(this.x);
}

}


And, 'Complex' looks like:-

public class Complex extends Field
{
// instance variables
private double x;
private double y;

public Complex(double a, double b)
{
super(a, b);
}

public double getValue()
{
return(0.0);
}
}


Now, my problem is, is that I want the version of 'getValue()' in the Complex class to have a different return type than 'double'.Possibly for it to have either a 'void' or an error message.

I have tried messing around with generics, and also 'covariant return types', but cannot seem to get either to work without the compiler complaining. Any ideas appreciated.