I have this scenario:
class ClassB{
ClassB(){
ClassA a = new ClassA(() -> a.foo());
}
}
class ClassA{
ClassA(Runnable onChange) {
}
public void foo(){
System.out.println("Hello");
}
}
And I get "Variable 'a' might not have been initialized". I understand why this is happening. Is there a work around or do I have to restructure my classes?
Without changing any of your types, this should work:
class ClassB {
ClassB() {
AtomicReference<A> ref = new AtomicReference<>(); // holder for instance
ClassA a = new ClassA(() -> ref.get().foo());
ref.set(a);
}
}
But you cannot invoke your lambda (Runnable#run) in your constructor, because a still has the value null. Only after the constructor has completed, the value is assigned.
Another possibility could be using a Consumer instead of a Runnable:
class ClassB {
ClassB() {
ClassA a = new ClassA(that -> that.foo()); // or maybe even: A::foo
}
}
class ClassA {
ClassA(Consumer<A> onChange) {
}
public void foo() {
System.out.println("Hello");
}
}
// call outside of `A`:
consumer.accept(a);
// or, inside of `A`:
consumer.accept(this);
Without seeing the rest of the code, it is difficult to give a good solution.
a variable is not intialised and that means it cannot be passed to the lambda.
AtomicReference to hold the value. The same limitations wrt. to call order still apply (you cannot call the lambda before the constructor has returned).I think you should consider refactoring your code and use a different approach. It's hard to tell without the full code but I suspect the design is not optimal.
With that said, here is something you could do which is similar to your approach.
Make ClassA Runnable and abstract:
abstract class ClassA implements Runnable{
private final Runnable onChange;
protected ClassA() {
this.onChange = this;
}
public void foo(){
System.out.println("Hello");
}
}
In ClassB you can implement an anonymous ClassA:
class ClassB {
ClassB() {
ClassA a = new ClassA() {
@Override
public void run() {
foo();
}
};
}
}
ais unused, andonChangeis unused.foo()method inside of theClassAconstructor implementation?setOnChangemethod. Anyway, you need to come up with a minimal reproducible example. Right now your code does nothing, so one way to fix it, while maintaining the behaviour (doing nothing) is to just remove the line with the error. Hopefully you see why this question is too broad.