In the next four lessons, we'll refactor "bad" code and replace it with an interface. You're in an org that has this BusinessAccount class:

public class BusinessAccount {

    Account accRecord; 

    public BusinessAccount(Account a){
        this.accRecord = a;
    }

    public void placeOrder(Order o){
        if(isValidOrder(o)){
            InvoiceGenerator.sendNewInvoice(accRecord, o); 
        }
    }

    private Boolean isValidOrder(Order o){
        Boolean isValid = false;
        // Validation logic specific to business accounts
        // isWithinCreditLimit()
        // hasOverdueInvoice() 
        return isValid;
    }
    
}

It's a wrapper for the Account sObject. Business accounts have their own unique process for validating and placing orders.

There is also a class named PersonAccount. It's also a wrapper for the Account sObject, but it represents a person, not a business. It's placeOrder and isValidOrder methods are different as a result:

public class PersonAccount {

    Account accRecord; 

    public PersonAccount(Account a){
        this.accRecord = a;
    }

    public void placeOrder(Order o){
        if(isValidOrder(o)){
            CreditCardEngine.chargeCardOnFile(accRecord, o); 
        }
    }

    private Boolean isValidOrder(Order o){
        Boolean isValid = false;
        // Validation logic specific to person accounts
        // isCreditCardOnFile()
        // doesExceedOrderLimits()
        return isValid;
    }
    
}

You're asked to build a common controller class to share between business and person accounts. See the challenge below for details.