CODEWITHSUNDEEP
javaclassconstructorinstances
Fofole
Fofole

Reputation: 3548

Java classes and constructors

I hope this won't sound like a stupid question.

I have a class A and a class B. Now the only thing B has is a String ID. Now I can have multiple objects A that each can have 0 or more objects of type B. These are contained in a HashMap(ID,someData) each class A has.

What I want to do is each time I add a new ID in class A to check whether there already is a on object of Type B with the same ID in any of the other class A objects I have, and if not, create a new B object.

Hope this makes sense. If what I ask is wrong is some way, please be kind enough to explain how is this a bad practice or conceptualy wrong.

Thanks a lot.

EDIT:To be more clear,in my case, it is not desireable to share the HashMap(ID,someData) for all my objects as for example let's say A is a Course class,Or Catalogue, or Bank etc. Each A class may share some students/clients but each A class may contain different class B objects.

Upvotes: 4

Views: 168

Answers (5)

gyurix
gyurix

Reputation: 1086

You should loop through all your A instances and use Hashmaps containsKey method to check that the new B value is already stored or not. If you only need to store all the B values to every A class only once, you can add a static modifier for your HashMap field.

Upvotes: 0

kgiannakakis
kgiannakakis

Reputation: 104168

If I were you I would have created a B_Factory class. This class would be responsible for creating the B objects. A class objects would call B_Factory methods to add or delete a B object. Inside B_Factory, you could use a Map to store the instances of B objects.

There should be only one instance of B_Factory class, which will be injected in all A instances.

Upvotes: 0

Murat Derya Özen
Murat Derya Özen

Reputation: 2154

To achieve your purpose, you can make the HashMap a static variable, instead of an instance variable. Therefore, it will be shared among all instance of Class A.

Upvotes: 0

Peter Lawrey
Peter Lawrey

Reputation: 533482

The thing you need to do this is to have a collection of all A objects so you can check them all. As you get more A objects this will become more inefficient. A diiferent was to structure this might be to use the ID as you collection.

Map<ID,/* class with A and someData *> map = ...

This allows you to ensure uniqueness of ID across all A.

Upvotes: 0

Luchian Grigore
Luchian Grigore

Reputation: 258558

It's not bad practice, it seems like you're implementing the Instance Manager Pattern.

  • Ability to look up one or more instances (via a key) of the managed object(s). If only one managed object, then a key is not necessary.

Upvotes: 4

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