Constructor of arrays

Question

Hello everybody
I've recently created a new class called Patient. I've now created a second class called Statistic.
In the second class I've decided to declare, as a data member an array of type Patient.
Because there will be only one array, so I have chosen to declare the data member static (the methods in the Statistics class will also be static).
I was simply wondering when I create the array I will write:
Patient [ ] patientTable=new Patient [100];
After this is done do I absolutely need a constructor because I've learned that if there is no constructor, default values are assigned; or is it better programming practice to have a constructor? Does the creation of the array have to be done in the constructor and then initialised with a for loop, for example. Shou;d the constructor have any parameters of type Patient for example. I'm not really sure how to create and initialise my array in the Statistic class.
There will be a third class eventually (main class) where the data will be inputted, Patient instances created and then called one after the other to fill the array, where calculations will be performed and then sent back to the main application.
Thank you for your time

Answer 1

Hello everybody
I've recently created a new class called Patient. I've
now created a second class called Statistic.Excellent!
>
In the second class I've decided to declare, as a data
member an array of type Patient.So a Statistic has many Patients? I would think it more likely that a Patient would have many Statistics.
Because there will be only one array, so I have chosen
to declare the data member static (the methods in the
Statistics class will also be static).Array of what? This isn't clear.
What is the Statistics class doing? Providing functions to calculate mean, standard deviation, etc., a la java.lang.Math and its sine and consine functions?
>
I was simply wondering when I create the array I will
write:
Patient [ ] patientTable=new Patient [100];Yes, this will create an array of 100 references to Patient, and every single one of them will be set equal to null until you call a Patient constructor to point them to a valid Patient instance.
After this is done do I absolutely need a constructor
because I've learned that if there is no constructor,The compiler will write a no-argument default constructor for you. It allocates memory for your object and assigns initial values for every data member. Primitives are given their default values, and object references are set to null.
If this default behavior isn't acceptable (and having null data member references usually isn't), you'll have to write a sensible constructor or two of your own. The instant you supply even one constructor the compiler will no long write the default constructor for you.
default values are assigned; or is it better
programming practice to have a constructor? Does the
creation of the array have to be done in the
constructor and then initialised with a for loop, for
example. Yes, absolutely:
int maxPatients = 100;
Patient [] patients = new Patient[maxPatients];
for (int i = 0; i < maxPatients; ++i)
    patients[i] = new Patient(name, rank, serialNumber);
Shou;d the constructor have any parameters of
type Patient for example. I'm not really sure how to
create and initialise my array in the Statistic class.
There will be a third class eventually (main class)
where the data will be inputted, Patient instances
created and then called one after the other to fill
the array, where calculations will be performed and
then sent back to the main application.Hard to answer this bit without knowing more about your problem. It sounds like the Patient object will use the Statistic class to perform calculations on some data that you haven't described.
Why a fixed-length array of Patients? Why not a java.util.List of Patients that can accomodate an arbitrary number of Patients?
This design can get complicated fast. A Patient might have many measurements taken during a typical hospital stay (e.g., weight, height, blood pressure, heart rate, etc.) You might want a Quantity class that will combine the value with the type of measurement and the units used (weight can be lbf in the USA or kg in Europe). When you calculate Statistics you'll want to make sure that you add Quantities of the same type and units. LOTS of complications here. Martin Fowler's "Analysis Patterns" has a lot of info on this and other problems if you're interested.