When gets the static initializer of a private static class exectuted?

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joes - 09 Jan 2008 07:38 GMT

Hello Gurus

I have a question. I have a class which holds an inner class declared
"private static". This inner class has a static field which is
immediately initilaized. When gets this static initilaziation of a
private static class exectuted?

- does it get executed when the outer class is loaded?
- does it get only executed if the inner class is getting loaded?

Example:
------------
public class Log {

private static class LoggerHolder {
public static Logger sLogger =
LoggerHelper.getLogger(LOGGER_CLASS);
}

public static Logger getLogger() {
return LoggerHolder.sLogger;
}
}

many thanks
regards

Mark

Reply to this Message

Mike Schilling - 09 Jan 2008 09:49 GMT

> Hello Gurus
>
> I have a question. I have a class which holds an inner class
> declared
> "private static". This inner class

Nitpick. It's not an inner class. Inner classes may not have static
fields. It's a "nested" class.

> has a static field which is
> immediately initilaized. When gets this static initilaziation of a
> private static class exectuted?
>
> - does it get executed when the outer class is loaded?
> - does it get only executed if the inner class is getting loaded?

Only when the class which defines the static field gets loaded.

Reply to this Message

Lew - 09 Jan 2008 14:56 GMT

joes wrote:

>> I have a question. I have a class which holds an inner class
>> declared
>> "private static". This inner class

> Nitpick. It's not an inner class. Inner classes may not have static
> fields. It's a "nested" class.

>> has a static field which is
>> immediately initilaized. When gets this static initilaziation of a
>> private static class exectuted?
>>
>> - does it get executed when the outer class is loaded?
>> - does it get only executed if the inner class is getting loaded?

> Only when the class which defines the static field gets loaded.

Only when the first object of the nested class type is used. This is the
basis for a thread-safe lazy-loading idiom much ballyhooed by Brian Goetz, et al.
<http://www-128.ibm.com/developerworks/java/library/j-jtp03304/>
Within the outer class:

> private static class LazySomethingHolder {
> public static Something something = new Something();
[quoted text clipped - 5 lines]
> return LazySomethingHolder.something;
> }

The nested class's static initializer is not run when the outer class is
loaded but when the getInstance() method is first called.