Question

What does

static{
    //something
}

declared inside a class definition body mean?

public class A extends B{
     static {
          C.register(new C(A.class,
                    (byte) D.x.getCode()) {
                         public DataSerializable newInstance() {
                              return new A();
                         }
                    }
               );
     }
 }

Answer 1

The static block is called a “static initialization block.” It is very similar to a regular constructor except that it can only initialize static variables.

I have found it to be useful when initialization of some static variable may throw an exception that you would like to handle or at least log. It is especially useful in the initialization of static final variables.

You may read more about static initialization blocks here: Initializing Fields