InstantiationException on simple reflective call to newInstance on a class?

java reflection instantiationexception
mburke13 picture mburke13 · Oct 26, 2011 · Viewed 20.6k times · Source

I have an abstract class A, i.e.

public abstract class A {

    private final Object o;

    public A(Object o) {
        this.o = o;
    }

    public int a() {
        return 0;
    }

    public abstract int b();

}

I have a subclass B, i.e.

public class B extends A {

    public B(Object o) {
        super(o);
    }

    @Override
    public int a() {
        return 1;
    }

    @Override
    public int b() {
        return 2;
    }

}

I am executing the following piece of code:

Constructor c = B.class.getDeclaredConstructor(Object.class);
B b = (B) c.newInstance(new Object());

and getting an InstantiationException on the call to newInstance, more specifically:

java.lang.InstantiationException
    at sun.reflect.InstantiationExceptionConstructorAccessorImpl.newInstance(InstantiationExceptionConstructorAccessorImpl.java:30)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:513)

I don't know why I'm receiving the exception. I have looked at some other similar questions and seen things about the usage of final variables when calling the super constructor or problems with the abstract nature of the parent class, but I could not find a definitive answer to why this particular situation throws an InstantiationException. Any ideas?

Answer

Brett Kail picture Brett Kail · Oct 26, 2011

Are you certain that B is not defined with the abstract keyword? I can reproduce the error if I declare the class as public abstract class B.

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