When does static class initialization happen?

Question

When are static fields initialized? If I never instantiate a class, but I access a static field, are ALL the static blocks and private static methods used to instantiate private static fields called (in order) at that instant?

What if I call a static method? Does it also run all the static blocks? Before the method?

Answer 1

A class's static initialization normally happens immediately before the first time one of the following events occur:

• an instance of the class is created,
• a static method of the class is invoked,
• a static field of the class is assigned,
• a non-constant static field is used, or
• for a top-level class, an assert statement lexically nested within the class is executed¹.

See JLS 12.4.1.

It is also possible to force a class to initialize (if it hasn't already initialized) by using Class.forName(fqn, true, classLoader) or the short form Class.forName(fqn)

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^{1 - The final bullet point was present in the JLS for Java 6 through Java 8, but it was apparently a mistake in the specification. It was finally corrected in the Java 9 JLS: see source.}