自己类中的对象

Question

So let's say:

public class Sample {  //main() class
    public static void main(String[] args) {
      A a = new A();
    }
}

public class A {
  A aa = new A();
}

1. So...when I run it ...it gives : java.lang.StackOverflowError. So, my explanation is that object a generation at line 1, furthers creates object aa generation at line 2...and then it enters a recursion .... which keeps creating object after object, until the heap memory is full.

2. If the objects are created on Heap...then why does it say StackOverflowError ??

Answer 1

Well, it's using both heap and stack. The stack space is because you're in the constructor for A , recursively. It would be simpler to see this if you put the initialization in the body of the constructor:

public class A {
  A aa;

  public A() {
     aa = new A();
  }
}

So the A constructor calls itself, then calls itself, etc. There's generally rather more heap space available than stack space, hence why you're running out of stack space first. If your class had a lot of fields, you would conceivably run out of heap space first - although usually the heap is pretty huge in modern machines.

Answer 2

The reason for a stack overflow is simply that the stack runs out of space before the (small) As can fill up the heap.

You have correctly recognized the recursion. So!