Interfaces should not have side-effects and that even applies to static intializers. They would have highly JVM-implementation dependent behavior. Look at the following code
public class InterfaceSideEffects {
public static void main(String[] args) {
System.out.println("InterfaceSideEffects.main()");
Impl i=new Impl();
System.out.println("Impl initialized");
i.bla();
System.out.println("Impl instance method invoked");
Foo f=new Impl();
System.out.println("Impl initialized and assigned to Foo");
f.bla();
System.out.println("Foo interface method invoked");
}
}
interface Foo {
int dummy=Bar.haveSideEffect();
void bla();
}
class Bar {
static int haveSideEffect() {
System.out.println("interface Foo initialized");
return 0;
}
}
class Impl implements Foo {
public void bla() {
}
}
What do you think, when will interface Foo initialized
be printed? Try to guess and run code afterwards. The answer might surprise you.