gistfile1.java

// We have a lot of residences in our portfolio. There would probably be many methods in addition to this one.
public class Residence {
  // Accept a visitor object so it can do something
  void accept(Visitor visit);
}

// We have detached houses
public class DetachedHouse implements Residence {
  // imagine getters and setters for these values
  private double squareFeet;
  private int lotSizeFeet;
  
  @Override
  public void accept(final ResidenceVisitor visitor) {
    visitor.visit(this);  
  }
}

// We have condos
public class Condo implements Residence {
  // imagine getters and setters for these values
  private double squareFeet;
  private boolean hasView;
  
  @Override
  public void accept(final ResidenceVisitor visitor) {
    visitor.visit(this);  
  }
}

// This class will calculate the value of our portfolio
interface ResidenceVisitor {
  int visit(DetachedHouse detachedHouse);
  int visit(Condo condo);
}

// This class will calculate the value of our portfolio
public class CutterModelPortfolioCalculator implements ResidenceVisitor {
  // imagine getters and setters for this value
  private int portfolioValue;
  
  @Override
  public int visit(final DetachedHouse detachedHouse) {
    return (detachedHouse.getSquareFeet() * 2,000) + (detachedHouse.getLotSize() * 100);
  }
  
  @Override
  public int visit(final Condo condo) {
    int value = condo.getSquareFeet() * 1,000;
    
    if (portfolioValue.hasView()) {
      value += 10,000;
    }
    
    return value;
  }
}

// an example of how it could be executed
final CutterModelPortfolioCalculator visitor = new CutterModelPortfolioCalculator();
int portfolioValue = 0;
for (final Residence residence : residences) {
  portfolioValue += residence.accept(visitor);
}

System.out.println("Total portfolio value: $" + portfolioValue);