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The advantage of choosing this approach over the inheritance-based pattern is that instead of
tying the implementation of this algorithm into the LoanApplication hierarchy, we can be
much more flexible about where to delegate the functionality to. For example, we may de-
cide that our Company class should be responsible for all criteria checking. The Company
class would then have a series of signatures like Example 8-25 .
Example 8-25. The criteria methods on a Company
public void
void checkIdentity () throws
throws ApplicationDenied ;
public void
void checkProfitAndLoss () throws
throws ApplicationDenied ;
public void
void checkHistoricalDebt () throws
throws ApplicationDenied ;
Now all our CompanyLoanApplication class needs to do is pass in method references to
those existing methods, as shown in Example 8-26 .
Example 8-26. Our CompanyLoanApplication specifies which methods provide each cri-
public class
class CompanyLoanApplication
CompanyLoanApplication extends
extends LoanApplication {
public CompanyLoanApplication ( Company company ) {
super ( company: : checkIdentity ,
company: : checkHistoricalDebt ,
company: : checkProfitAndLoss );
A motivating reason to delegate the behavior to our Company class is that looking up inform-
ation about company identity differs between countries. In the UK, Companies House
provides a canonical location for registering company information, but in the US this differs
from state to state.
Using functional interfaces to implement the criteria doesn't preclude us from placing imple-
mentation within the subclasses, either. We can explicitly use a lambda expression to place
implementation within these classes, or use a method reference to the current class.
We also don't need to enforce inheritance between EmployeeLoanApplication and Person-
alLoanApplication to be able to reuse the functionality of EmployeeLoanApplication in
PersonalLoanApplication . We can pass in references to the same methods. Whether they
do genuinely subclass each other should really be determined by whether loans to employees
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