在超类构造函数中创建子类对象进入无限循环java

Question

This might be a silly question, but please bear with me for now. I have something similar to:

     public class A{


    public A(){
        //Some statements here

        B bObj = new B(); //Goes in infinite loop this above statement

        (new Thread(bObj)).start();
        //Some statements here


    }

    public static void main(String[] args){
         A aObj = new A();

        }

    }
}

class B extends A implements Runnable{
    public testprint(){
        System.out.println("Inside testprint()");
    }
}

If I create a subclass object in the superclass, it goes in infinite loop, because I guess once subclass object is created it keeps calling superclass constructor which keeps creating subclass object. If I declare the subclass object in main, I get something like 'Cannot reference non-static member from static context' because my superclass object is not yet initialized. So I cannot initialize my subclass object in main.

So what would be a good way to deal with this?

Answer 1

A couple things I see going on that's wrong. First, as per the comments, you can't create an instance of B in the constructor of B's parent class. That would be an infinite loop.

Also, I see you call "new bObj". You meant new B() I assume?

You want to create an instance of B instead of A, then in B's constructor, when starting the thread, you'd want to pass "this" to the Thread object, rather than trying to create a new instance.

And lastly, you really shouldn't try starting the thread in the constructor anyway. You'd effectively be passing, to the Thread class, an object that's not fully constructed yet. Should start it after the object is constructed.

Answer 2

Don't forget that every B is an A . So every time you try to create a B , you are in fact creating an A .

Now look at your code again. In your constructor for A , which of course gets called every time you create an A , you've said "start by creating an A ". Were you not expecting an infinite loop?