Interpreting the "Incompatible argument to function" exception message

Question

A quick question regarding the java.lang.VerifyError exception. Suppose I get an error that looks like this:

Java call terminated by uncaught Java exception: java.lang.VerifyError:(class: com/.../MyClassName, method: <init> signature: (Ljava/io/Reader;)V) Incompatible argument to function

Could you help me with understanding what the "init" and what the "(Ljava/io/Reader;)V)" parts pertain to? They don't look like method names or signatures to me, but I'm not too familiar with java. Thanks!

Pilsudski

Answer 1

This error means that somewhere in your code, you tried to call a constructor (the <init> method) passing in the wrong set of arguments. The expected argument was a Reader object.

This probably meant that you previously compiled a class file, then changed the class definition in some way without recompiling the class file. Consequently, your code tries to call a function that no longer exists. Try recompiling the code and see if that fixes it.

Hope this helps!

Borrowing

Thanks! The problem is, the type of the object being initialized does have two constructors, one taking a string and one taking a StreamReader as a parameter. There is no other version of the type that is missing the constructor that takes a string. This is bizarre. I have to find a way to step through this code. – Pilsudski

We finally figured out that the loaded java classes were corrupt and had to force a reload of all the classes. – Pilsudski

Answer 2

If you are running your application on an application server, it could be a class loading problem.

You compiled your code against a library and when you try to run your code it is running against a different (older?) version of the library.

The older library probably doesn't have that method or constructor.

Unscrupulous

Thanks. I do agree it is likely related to a version mismatch. – Pilsudski

Answer 3

Just to leave track of a different cause.

Always on an application server (in my case WildFly 10), you might be loading the same library on a modules and on the EAR lib. If this library contains an interface that needs to be implemented by the module, this might cause a conflict since the same class / interface loaded by two different class loaders are considered to be two different types.

Tigrinya