How i would create multiple instances of different classes in an easy way?

Question

I'm searching a way to creating different instances of different classes without writing a hacky code like:

PersonInstance pinstance = new PersonInstance();
FamilyInstance finstance = new FamilyInstance();

But with doing this it can go too far numbers of instances (like 70). Any ideas on how to make a good code without writing 70 lines that having the same sort of codes? If you didn't understand:

Initializing 70 different instances (different classes, everything different) with the classic method

PersonInstance instance = new PersonInstance();

for 70 times (different class, different instance identifier) is a bit hacky. I would like to know how to initialize them without using that way. Clearly all the classes have something common thing that they all extends on the same class. I want to know if it's possible or not?

you can use factory design pattern to create the object you want.object creation can be wrap around for loop. — gihan-maduranga, Dec 25 '16 at 18:17
I really do not know which of the several alternatives that come to my mind you mean, you should be more specific. Each of these are assigned into separate local variables. Is your code going to have 70 separate variables? — Antti Haapala -- Слава Україні, Dec 25 '16 at 18:18
@SapusBoh no, we don't. I don't see what is hacky here. It's plain simple, straightforward Java code. Why do you need 70 different variables referencing 70 objects of 70 different types in the first place? — JB Nizet, Dec 25 '16 at 18:19
@gihan How i could do it? Never heard these factory design patterns.. — Sapus Boh, Dec 25 '16 at 18:19
@AnttiHaapala i just need to initialize them, after, i don't need to do other. — Sapus Boh, Dec 25 '16 at 18:20
@gihan Basically, i have to inizialize 70 classes for let them generate files etc. The problem is that creating 70 times an instance with the classic method (See first post) it's a bit hacky. — Sapus Boh, Dec 25 '16 at 18:23
What does "initializing a class" mean? Could you show an example of 2 of those classes? — JB Nizet, Dec 25 '16 at 18:24
No, they're not. Show is the code of PersonInstance and the code of FamilyInstance. But you can also ignore all the requests from people trying to understand your question, and waiting for it to be closed because it's unclear. — JB Nizet, Dec 25 '16 at 18:28
you can use `for loop` to create the class objects.you mentioned that all classes are inherited from base class let say `person`.so when your creating you can create class something like `Person p=new FamilyInstance()` and when you use it you have to check if reference class is actually a `FamilyInstance` before used it methods. — gihan-maduranga, Dec 25 '16 at 18:37

score 1 · Answer 1 · edited May 23 '17 at 10:30

1

If the classes are interrelated i.e inheritance then make an array. Visit C++ create array of objects (from different classes)

edited May 23 '17 at 10:30

Community

1
1

answered Dec 25 '16 at 18:22

skag

170
11

Thank you for the answer, but i'm searching a way with java. – Sapus Boh Dec 25 '16 at 18:26

score 0 · Answer 2 · answered Dec 25 '16 at 19:16

If I understand this correct, you have to create a superclass for all your different classes. Example:

class B extends PersonInstance
{
//
}
class C extends PersonInstance
{
//
}

Then, you have to create an array or a list for example:

List<PersonInstance> list = new ArrayList<>();
for(int i = 0; i<=69; i++)
{
    list.add(new B());
    // or list.add(new C());
}

score 0 · Answer 3 · answered Dec 25 '16 at 19:37

You could use Dependency injection/Inversion of Control (IoC). For example Spring comes with annotations like @Autowire to put over your constructor.. The Dependency Injection Container does all the initializations parsing all the dependencies and passing them to the proper constructors without the need to call new yourself . The code becomes cleaner and easier to Unit Test..I will add links later when I am on a PC :)

CJR · Answer 4 · 2016-12-26T15:28:28.530

Instead of doing this:

PersonInstance instance1 = new PersonInstance();
PersonInstance instance2 = new PersonInstance();
...
...
...
PersonInstance instance99 = new PersonInstance();

You could use an array to create all 70 instances of PersonInstance, like:

PersonInstance[] personInstances = new PersonInstance[N];
for(int i = 0; i < personInstances.length; i++){
    personInstances[i] = new personInstances();
}

Where N is the number of slots in the array where you could store instances of PersonInstance. In your case, N would be 70:

PersonInstance[] personInstances = new PersonInstance[70];
for(int i = 0; i < personInstances.length; i++){
    personInstances[i] = new personInstances();
}

Then if you would like to access PersonInstance number k, you would do so by:

PersonInstace thisPerson = personInstances[k-1];

since an array start from index 0, e.g if you want to access PersonInstance 56, you would do so by:

PersonInstace thisPerson = personInstances[55];

Hope it helps.

UPDATED ANSWER:

If for example, BrotherInstance extends PersonInstance, you could add a BrotherInstance to your PersonInstance array like:

PersonInstance[] personInstances = new PersonInstance[70];
    //add 50 PersonInstances
    for(int i = 0; i < personInstances.length-20; i++){
        personInstances[i] = new PersonInstances();
    }
    //add 20 BrotherInstances
    for(int i = 50; i < personInstances.length; i++){
        personInstances[i] = new BrotherInstances();
    }

And access them one by one like:

PersonInstance currentPerson = personInstances[24]    //A PersonInstance
PersonInstance currentBrother = personInstances[61]   //A Brother instance

or

BrotherInstance currentBrother = personInstances[61]   //A Brother instance

or loop them all like:

for(PersonInstance person: personInstances){
        //Do something with every person here, maybe print out something.
    }

That for-loop will loop through all PersonInstances, wether they are PersonInstance or BrotherInstance since they are either a PersonIntance or extend PersonInstance.

But if you need to create a different instance like 1 family instance, 1 person instance, 1 brother instance etc.? — Sapus Boh, Dec 25 '16 at 20:15
Does the other instances e.g BrotherInstance extend personinstance? Could you share the code for them? @SapusBoh — CJR, Dec 25 '16 at 23:20
Yes, they all extend personinstance. Clearly these classes was an example. — Sapus Boh, Dec 26 '16 at 07:50
@SapusBoh Check out my updated answer under the "UPDATED ANSWER" section at the bottom. — CJR, Dec 26 '16 at 15:29

score -1 · Answer 5 · answered Dec 25 '16 at 19:22

-1

You can use the JAVA Reflection API, https://docs.oracle.com/javase/tutorial/reflect/member/ctorInstance.html

answered Dec 25 '16 at 19:22

bilelovitch

1,975
1
16
24

How i would create multiple instances of different classes in an easy way?

5 Answers5