94. Tackling guarded record patterns
Exactly as in the case of type patterns, we can add guarding conditions based on the binding variables. For instance, the following code uses guarding conditions with instanceof for determining if the Allergy cabinet is open or closed (you should be familiar with the Doctor record from the previous two problems):
public static String cabinet(Staff staff) {
if (staff instanceof Doctor(String name, String specialty)
&& (specialty.equals(“Allergy”)
&& (name.equals(“Kyle Ulm”)))) {
return “The cabinet of ” + specialty
+ ” is closed. The doctor “
+ name + ” is on holiday.”;
}
if (staff instanceof Doctor(String name, String specialty)
&& (specialty.equals(“Allergy”)
&& (name.equals(“John Hora”)))) {
return “The cabinet of ” + specialty
+ ” is open. The doctor “
+ name + ” is ready to receive patients.”;
}
}
If we add into the equation the Resident record as well then we can write this:
if (staff instanceof Resident(String rsname,
Doctor(String drname, String specialty))
&& (specialty.equals(“Dermatology”)
&& rsname.equals(“Mark Oil”))) {
return “Cabinet of ” + specialty + “. Doctor “
+ drname + ” and resident ” + rsname
+ ” are ready to receive patients.”;
}
And, if we add the Patient and Appointment records as well then we can check if a certain patient has an appointment as follows:
public static String reception(Object o) {
if(o instanceof Patient(var ptname, var npi,
Appointment(var date,
Doctor (var drname, var specialty)))
&& (ptname.equals(“Alicia Goy”) && npi == 1234567890
&& LocalDate.now().equals(date))) {
return “The doctor ” + drname + ” from ” + specialty
+ ” is ready for you ” + ptname;
}
}
When we are using record patterns with guarded conditions in switch expressions things are straightforward. The mention consists of using the when keyword (not the && operator) as in the following code:
public static String cabinet(Staff staff) {
return switch(staff) {
case Doctor(var name, var specialty)
when specialty.equals(“Dermatology”)
-> “The cabinet of ” + specialty
+ ” is currently under renovation”;
case Doctor(var name, var specialty)
when (specialty.equals(“Allergy”)
&& (name.equals(“Kyle Ulm”)))
-> “The cabinet of ” + specialty
+ ” is closed. The doctor ” + name
+ ” is on holiday.”;
case Doctor(var name, var specialty)
when (specialty.equals(“Allergy”)
&& (name.equals(“John Hora”)))
-> “The cabinet of ” + specialty
+ ” is open. The doctor ” + name
+ ” is ready to receive patients.”;
case Resident(var rsname,
Doctor(var drname, var specialty))
when (specialty.equals(“Dermatology”)
&& rsname.equals(“Mark Oil”))
-> “Cabinet of ” + specialty + “. Doctor “
+ drname + ” and resident ” + rsname
+ ” are ready to receive patients.”;
default -> “Cabinet closed”;
};
}
And, if we add the Patient and Appointment records as well then we can check if a certain patient has an appointment as follows:
public static String reception(Object o) {
return switch(o) {
case Patient(String ptname, int npi,
Appointment(LocalDate date,
Doctor (String drname, String specialty)))
when (ptname.equals(“Alicia Goy”)
&& npi == 1234567890 && LocalDate.now().equals(date))
-> “The doctor ” + drname + ” from ” + specialty
+ ” is ready for you ” + ptname;
default -> “”;
};
}
The JDK 19+ context-specific keyword when is added between the pattern label and the refining boolean checks to avoid the confusion of using the && operator.