CODEWITHSUNDEEP
javaenumsconstructor
Jonothan Ogden
Jonothan Ogden

Reputation: 1

Telling a enum what sub class type to use

Hello to explain what i am trying to do its best i show you

public class Main {

public enum Types{
    ONE(One.class),TWO(Two.class),THREE(Three.class);

    Class<?> type;

    private Types(Class<?> type) {
        this.type = type;
    }


}

public class Manager {
    ArrayList<Number> numbers = new ArrayList<>();

    public void Load() {
        //THIS IS WHERE I AM STUCK
        //I know it can be done like this below to add them in to the array with the types
        numbers.add((One) new Number());
        numbers.add((Two) new Number());
        numbers.add((One) new Number());
        numbers.add((Three) new Number());

        //But i want to be able to add them like this.
        numbers.add(Types.ONE.type.newInstance());

    }

    public void Run() {

        if (numbers.isEmpty()) {
            Load();
        }

        for (Number n : numbers) {
            n.call();
        }
    }
}

public class Number {
    public void call() {

    }       
}

public class One extends Number {   
    @Override
    public void call() {
    }
}

public class Two extends Number {   
    @Override
    public void call() {
    }
}

public class Three extends Number { 
    @Override
    public void call() {
    }
}

}

If you look for the comments in the code i am trying to add the "Number" to the array but with is sub class.

Now this is a example in the application i want it for the objects have parameters in the constructors. Can any one point me in the right direction.

The reason i just do not add them by using .add is in the real application there are 100s of objection to add to the array list and when i get these object there stored with there enum to show what type they are. Also these objects get changed regularly.

Upvotes: 0

Views: 55

Answers (1)

rgettman
rgettman

Reputation: 178263

Currently the variable type in Types is of type Class<?>. This Class object could represent any class object, which is not necessarily in the Number class hierarchy you've created.

Any object returned by newInstance could be of any type, so it can't be allowed by the compiler to be sent to an ArrayList<Number> as a parameter; it might not match.

Add an upper bound to the type of type:

enum Types{
    ONE(One.class),TWO(Two.class),THREE(Three.class);

    // add ? extends Number here
    Class<? extends Number> type;  

    // add ? extends Number here
    private Types(Class<? extends Number> type) {  
        this.type = type;
    }
}

You'll still have to catch all of the reflection-related exceptions: IllegalAccessException and InstantiationException.

Also note that in Java 9+, Class.newInstance is deprecated; you should replace that call with

getDeclaredConstructor().newInstance()

which also throws NoSuchMethodException and InvocationTargetException.

Upvotes: 2

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