Tips for initializing static constants using double parentheses in Java _java

This seems to be an unknown language skill. I see people writing java. Initializing static constants are all

Copy Code code as follows:

public static final map<string, string> DATA = new treemap<string, string> ();

Static
{

Data.put ("A", "a");

blah blah blah
}

Use the static block of the class to initialize data, but there is another way to do it:

Copy Code code as follows:

public static final map<string, string> DATA = new treemap<string, string> ()
{{

This.put ("A", "a");

blah blah blah

}};

This actually utilizes the attributes of the anonymous class, the inner {is used as the constructor of the anonymous subclass, so you can insert the initialization code directly, this small language technique is not common, but more practical.