How do I get only instantiable classes with reflections

Question

I am using the reflections package to get a set of classes that implement a certain interface. This set will be used as a list of possible command line options. My problem is that I only want to get instantiable classes, but right now get both instantiable and non-instantiable classes (e.g. abstract classes) from the following code:

Map<String, Class<? extends InterfaceOptimizer>> optimizerList = new HashMap<String, Class<? extends InterfaceOptimizer>>();

Reflections reflections = new Reflections("eva2.optimization.strategies");
Set<Class<? extends InterfaceOptimizer>> optimizers = reflections.getSubTypesOf(InterfaceOptimizer.class);
for(Class<? extends InterfaceOptimizer> optimizer : optimizers) {
    optimizerList.put(optimizer.getName(), optimizer);
}

Is there a way to filter the set returned by getSubTypesOf to filter out the abstract classes?

See http://stackoverflow.com/questions/1072890/how-can-i-determine-whether-a-java-class-is-abstract-by-reflection — rusmus, Oct 08 '13 at 13:47
@rusmus, I specifically asked for non-instantiable classes and abstract classes are only one example of that. Granted, the question you linked covers abstract classes pretty well, but I didn't know how to check for interfaces. — halfdan, Oct 08 '13 at 14:03
This is not a duplicate question. It asked about Reflections (and gave a link), not reflection. — whistling_marmot, May 21 '21 at 13:17

score 25 · Accepted Answer · answered Oct 08 '13 at 13:52

25

Use the isInterface() method to differentiate between classes and interfaces.

Use Modifier.isAbstract( getClass().getModifiers() ); to tell whether the class is abstract or not.

answered Oct 08 '13 at 13:52

Adam Arold

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if(Modifier.isAbstract( myclass.getModifiers() ) || myclass.isInterface()) – fl0w Feb 05 '18 at 16:23

score 8 · Answer 2 · answered Oct 08 '13 at 13:51

8

You can try this

cls.getModifiers() & Modifier.ABSTRACT == 0 && !cls.isInterface()

besides it makes sense to check if the class has a no-args constructor

answered Oct 08 '13 at 13:51

Evgeniy Dorofeev

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Thanks! Would love to accept your answer as well, but picked Adams simply because I prefer the isAbstract method. – halfdan Oct 08 '13 at 14:31

How do I get only instantiable classes with reflections

2 Answers2