Java 7中的静态初始化

Question

I have a code which initializes a class as:

private static MyClass myObj = new MyClass();

And I am using myObj in my code below. This works fine if Java 6 is used . But when I use Java 7, NullPointerException is thrown.

java.lang.NullPointerException
Exception in thread "main" java.lang.ExceptionInInitializerError

As a work around, I put a null check for myObj before using it and made it work.

But I am still confused if there is any changes in Java 7 implementation that made static initialization fail?

EDIT : Found similar issue was faced by OpenAM .

Answer 1

We'll need more code sample and exception stacktrace to diagnostic.

Pure speculation, I know that in Java 7, they changed class initialization a little bit

https://docs.oracle.com/javase/specs/jls/se7/html/jls-12.html#jls-12.4.2

For each class or interface C, there is a unique initialization lock LC. The mapping from C to LC is left to the discretion of the Java Virtual Machine implementation. The procedure for initializing C is then as follows:

1. Synchronize on the initialization lock, LC, for C. This involves waiting until the current thread can acquire LC.

this is different from previous java where the class object itself is used as the lock.

Still, it's quite unlikely that it's responsible for your case.

Answer 2

You could try:

public class X {

   private static MyClass myObj;

   static {
      myObj = new MyClass();
   }

}

Altough the static method is usually used to perform multiple operations