A tip for initializing static constants using double brackets in JAVA

This seems like an unknown language skill. I've seen that the average person who writes Java initializes static constants is

public static final Map<String, String> DATA = new TreeMap<String, String>();
static
{
DATA.put("a", "A");
//blah blah blah
}

Using the static block of the class to initialize DATA, there is another way to write it:

public static final Map<String, String> DATA = new TreeMap<String, String>()
{{
this.put("a", "A");
//blah blah blah
}};

This actually takes advantage of the nature of anonymous classes. The inner {is used as a constructor for anonymous subclasses, so you can insert the initialization code directly.