Question

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Static Initialization Blocks
Unusual “static” method declaration

I’m trying to prepare for a OCJPC in the near future, and I came across a construct I had never seen before. As it is tough to google for programming constructs, I am asking the question here. The code fragment:

class Geryon {
    static { System.out.print("a"); }
    { System.out.print("b"); }
    Geryon(String s) { System.out.print(s); }

    public static void main(String[] args) {
        new Geryon("c");
    }
}

I am referring to the 2 print statements inside theGeryon() method header in the place where I would expect a return type. As far as I was able to google, a static method header consists of:

access-modifier keyword-"static" return-type|void method-name

Judging from the answer to the quiz question, the code does not only compile, but will also be run. Can anyone direct me to a source where this is explained?

Answer 1

A is a static initializer that gets called when the class is initialized by classloader, this :

 static { System.out.print("a"); }

And the other (B) is an anonymous block that gets called every time the class is instantiated :

{ System.out.print("b"); }

Oh and the third print statement, C, is just a normal constructor call.

You will get all three lines if you instantiated one Geryon, like the code you posted. But then the next time you instantiated a Geryon you will only get two – B and C; as it has already been initialized by classloader, so the static block does not get called.