[roots]

It ain't ruby !!
You can achieve this using call back, mess of codes ..

Code:

public class Main {
	double initialCost ;
	CostCalculator cost1 ;
	CostCalculator cost2 ;
	
	Main(){
		cost1 = new CostCalculator(){
			@Override
			public double Calculate(double initialCost) {
				return initialCost * 2 ;
			}
			
		};
		
		cost2 = new CostCalculator(){
			@Override
			public double Calculate(double initialCost) {
				return initialCost * 3 ; // What ever
			}			
		};	
	}
	
	public double calculate(){
		return cost1.Calculate(initialCost); // Plus extra stuffs if you have
	}
}

If i have understood your problem correctly, this is one of the option you have got.