design patterns - In Java, why have a code block with no keywords, just curly brackets

Question

I'm re-factoring some inherited code, but was stumped by the design decision and can't figure out the proper terms to google this. My predecessor would use blocks like this one:

public class ChildClass extends ParentClass {
    {
        inheritedVar = "someVal";
    }

    public ChildClass(){ /* constructor exists */ }
    // rest of code
}

What is the point of declaring a block of code with no keyword? It doesn't behave like a static block, I don't believe. Is it an alternative to setting in the constructor? Would this have some effect if a factory was being used (which in this case it's not)? I found a related thread here on this happening in C but the reasoning (scope & variable declaration) didn't seem relevant to Java.

Any thoughts or ideas on the "why" of this would be appreciated. It's easy enough to re-factor this, I'm just curious at this point.

Answer 1

It is an initializer block. (Related to static initializer block) See Initializing Instance Members on this page:

http://download.oracle.com/javase/tutorial/java/javaOO/initial.html

It is an alternative to a constructor. You could use it when providing multiple, overloaded constructors as a way to share code.

Personally, however, I find it much clearer to have the constructor call a named initializer method rather than rely on the anonymous code block. Although, the compiler does copy the initializer block to all constructors behind the scenes and you could argue that there is a performance increase similar to inline'ing a method declaration.