Passing "this" in java constructor

Question

Look into the following code:

public class ClassA {
    private boolean ClassAattr = false;

    public ClassA() {    
        ClassAHandler handler = new ClassAHandler(this);
    }
}

public class ClassAHandler extends GeneralHandler {
    ClassA ca = null;

    public ClassAHandler(ClassA classa) {
        this.ca = classa;
    }
}

I need to access ClassAattr on some ClassAHandler methods, among other attributes. Is there a way to do so without passing the origin class in the handler constructor. I don't really like how this solution "looks".

Answer 1

Passing this to another method/object from inside the constructor can be rather dangerous. Many guarantees that objects usually fulfill are not necessarily true, when they are looked at from inside the constructor.

For example if your class has a final (non-static) field, then you can usually depend on it being set to a value and never changing.

When the object you look at is currently executing its constructor, then that guarantee no longer holds true.

As an alternative you could delay the construction of the ClassAHandler object until it is first needed (for example by doing lazy initialization in the getter of that property).