Reflection - Class implementing an interface as parameter

Question

I want to pass a Class as parameter and return an instance of this class. I need ensure that the class implements ISomeInterface. I know I can do it with reflection:

Object get(Class theClass) {
    return theClass.newInstance();
}

What I do not know is how to ensure that theClass implements ISomeInterface

ISomeInterface get(Class<? extends ISomeInterface> theClass) {...}
// errrr... you know what i mean?

I don't like reflection in production, but is it very handful for testing

Why is Class.newInstance() "evil"?

score 2 · Accepted Answer · answered Oct 21 '13 at 08:17

2

Use isAssignableFrom.

ISomeInterface get(Class<? extends ISomeInterface> theClass) {
    if (ISomeInterface.class.isAssignableFrom(theClass)) {
        return theClass.newInstance();
    } else { /* throw exception or whatever */ }
}

answered Oct 21 '13 at 08:17

sebastian_oe

7,186
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score 1 · Answer 2 · answered Oct 21 '13 at 08:16

1

Take a look here Class.isAssignableFrom(java.lang.Class c)

answered Oct 21 '13 at 08:16

Admit

4,897
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score 1 · Answer 3 · answered Oct 21 '13 at 08:34

You have to explicitly check whether the given class object is not of an interface. isAssignableFrom() will return true even if you have both the class objects of interfaces.Since they are on the same hierarchy, it will return true.

I suggest you to try the following code

ISomeInterface get(Class<? extends ISomeInterface> theClass) {
if(!clazz.isInterface()){
    if (ISomeInterface.class.isAssignableFrom(theClass)) {
        return theClass.newInstance();
    } else { /* throw exception or whatever */ }
}
}

score 0 · Answer 4 · answered Feb 13 '16 at 20:29

0

You can use generics:

public <T extends ISomeInterface> T get(Class<T> theClass) {
   return theClass.newInstance();
}

answered Feb 13 '16 at 20:29

mabg

1,894
21
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Reflection - Class implementing an interface as parameter

4 Answers4