getDeclaredConstructors（）返回java.lang.NullPointerException

Question

I'm using a java web framework (Vraptor) and I'm having the following problem: The frameworks uses Reflection to instantiate the Controllers parameters, and for some reason one of the Parameters is returing <java.lang.NullPointerException> .

My question is: the framework works normally for a while, and for some reason the "cachedConstructor" of the type I want to instantiate is filled with <java.lang.NullPointerException> instead of what is expected. What could possible make that change?

I'm not asking if the framework is doing this, I just want to know what could do this in Java

getClassType().getDeclaredConstructors() is return java.lang.NullPointerException (returning, not throwing)

Answer 1

Most likely getClassType() is returning a null value. If you debug through your code and put some console output for values, you'll see which value is coming back as null. Do some null value checking before you use an object, if required.

See What is a NullPointerException, and how do I fix it?