static method with static default code?

Question

Sorry for the bad title, but I found the code listed below on mkyoung.com and was wondering what this code does. Is this a way in Java to set some default value into a variable?

public class LanguageBean implements Serializable{
    private static Map<String,Object> countries;
    static{
        countries = new LinkedHashMap<String,Object>();
        countries.put("English", Locale.ENGLISH); //label, value
        countries.put("Chinese", Locale.SIMPLIFIED_CHINESE);
    }
}

Answer 1

This bit declares a static field:

private static Map<String,Object> countries;

So it's accessible directly on the class, e.g. LanguageBean.countries (or just countries), but only from code within the class, because it's private.

This bit is a static initializer:

static{
    countries = new LinkedHashMap<String,Object>();
    countries.put("English", Locale.ENGLISH); //label, value
    countries.put("Chinese", Locale.SIMPLIFIED_CHINESE);
}

That runs when the class is loaded, before any instances are created, and does indeed add some entries to countries. If there are multiple static initializers, they're run in source code order. See Static Initializer Blocks in this tutorial.

---

FWIW, there are also per-instance versions of both of those. An instance field:

private int foo;

...and an instance initializer; they look a bit weird, because they're just blocks with nothing in front of the block:

{
    this.foo = 42;
}

In context, and with a second instance member:

class Thing {
    private int bar = 16; // An initializer on the declaration
    private int foo;

    // An instance initializer block
    {
        this.foo = 42; // Or just foo = 42;, but I prefer to be clear
    }
}

So you can do the same sort of thing for instances.

Answer 2

Basically yes, it's formally called a static initializer. And per JLS-8.7 Static Initializers

A static initializer declared in a class is executed when the class is initialized (§12.4.2). Together with any field initializers for class variables (§8.3.2), static initializers may be used to initialize the class variables of the class.