`Calculator.java`
`01 package trail.entity.basic; 02 03 import trail.entity.beans.*; 04 import java.util.Collection; 05 06 public interface Calculator { 07 08 public void addFund (String name, double growthrate); 09 public void addInvestor (String name, int start, int end); 10 11 public double calculate (int fundId, int personId, double saving); 12 13 public Collection<Fund> getFunds (); 14 public Collection <Investor> getInvestors (); 15 public Collection <TimedRecord> getRecords (); 16 17 }`