Calculator Calculable

package ir.javacup.calc;

import java.math.BigDecimal;
import java.util.*;

public class CalculatorProxy implements Calculable {

	private final Calculable calculator;

    private Map <String,BigDecimal> sofar=new HashMap<>();

	public CalculatorProxy(Calculable calculator) {
		this.calculator = calculator;
	}

	@Override
	public BigDecimal doOperation(BigDecimal... operands) {
		String s="";
		BigDecimal ans=new BigDecimal(0);
		for(BigDecimal k:operands)
		{
			s=s+","+k.toString();
		}
		
		if(sofar.containsKey(s))
			return sofar.get(s);
		else
		{
			ans=calculator.doOperation(operands);
			sofar.put(s, ans);
			return ans;
		}
	}

}