Create object of unknown class

Question

I am searching for a solution to my problem for a while now but I cannot find an answer which is specific for my question. I have a Class A which is abstract and Class B and C which extends class A. A and B are concrete classes. Class A implements function which will be inherited by V and C. Inside this function I want to create new object of B or C - the problem is that I don't know which object is that.

How can I achieve this?

public void colision(List<Organism> organisms) {

    List<Organism> temp = new ArrayList<Organism>(organisms);
    temp.remove(this);

    for (Organizm organism : temp){
        if (this.location == organizm.getLocation()){
            if (this.getClass().equals(organism.getClass())){ 
                        //here is what I need to figure out
            }
            else{ 
                ...
                }
            }
        }
    }
}

Please explain in words how you decide which class you want. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented May 10, 2015 at 15:45
Add an abstract method createNewInstance() to A, and implement it in B and C. But you should really tell us what you're trying to achieve, at a higher level, because this.getClass().equals(organism.getClass())is a design smell. — JB Nizet
– JB Nizet, Commented May 10, 2015 at 15:45

Bananan · Accepted Answer · 2015-05-10 15:46:35Z

5

Use Class<T>.newInstance() e.g.: organism.getClass().newInstance(). In order to do that you need to have default constructor in your class definition otherwise you need to find constructor - e.g.: Constructor constructor = organism.getClass().getDeclaredConstructor(parameterTypes...); and then use it like constructor.newInstance(arguments...);.

answered May 10, 2015 at 15:46

Bananan

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1 Comment

Radiodef Over a year ago

Use organism.getClass().getConstructor().newInstance() for more informative exceptions.

pathfinderelite · Accepted Answer · 2015-05-10 15:45:49Z

0

Use the Factory design pattern

answered May 10, 2015 at 15:45

pathfinderelite

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Comments

Tony Vu · Accepted Answer · 2015-05-10 15:48:04Z

0

Probably you can have an abstract method getInstance() in A and then have both B and C implement that method

answered May 10, 2015 at 15:48

Tony Vu

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