InstantiationException on simple reflective call to newInstance on a class?
Solution 1
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
.
Solution 2
The newInstance() method actually doesn't take any args -- it only triggers the zero-arg constructor. It will throw InstantiationException if your class doesn't have a constructor with zero parameters.
mburke13
Updated on January 15, 2020Comments
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mburke13 over 4 years
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?
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mburke13 over 12 yearsNo, I'm not certain. For some reason I do have B declared as abstract (when it doesn't have any methods to be implemented). I assumed that I didn't so this must be just one of those mental slips. Apologies for the waste of time :/
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Buffalo almost 8 yearsThis was precisely my issue.. thanks for the heads up.