在外部类外部创建内部类对象时引用外部类对象

Question

Inner classes can be instantiated outside the outer class using Outer_class_object.new inner_class() . But the question arises what happens to Outer class object? means there is no reference variable referencing to it. Obviously it will be on the heap till the inner class object is on heap because Inner classes feed on outer class. So what mechanism java uses in such situations? See the following code...
What happens to the outer class object in the main of NormalInnerClassDemo that we used to create object of inner class. It has to stay alive till the 'inner' is alive.There is no reference variable referring to it doesn't that make it eligible for garbage collection ? If not how does Java manages to tell the garbage collector not to do so ?

class Outer {

    private String  string = "Google";

    class Inner {

        public Inner() {
            System.out.println("From Inner:" + string );
        }
    }

    public void test() {
        //Some code here
    }
}

public class NormalInnerClassDemo {

    public static void main( String[] args ) {
        Outer.Inner inner = new Outer().new Inner();
    }
}

Answer 1

Inner classes can be instantiated outside the outer class using Outer_class.inner_class.

No they can't. They are created via:

outer.new Outer.Inner(...)

where outer is a primary-expression that evaluates to a reference to an instance of Outer , for example new Outer(...) .

or

this.new Inner(...)

if you are inside Outer , or for short

new Inner(...)

if you are inside Outer .

But the question arises what happens to Outer class object? means there is no reference variable referencing to it.

Oh yes there is: see above.

Obviously it will be on the heap till the inner class object is on heap because Inner classes feed on outer class. So what mechanism java uses in such situations?

Your question is founded on a mistake.

Answer 2

First this is Java so why are you worried about heap memory when the VM cleans up for you? 8-)

To help you understand this, ADD the following to Outer class (default constructor):

Outer() {
  System.out.println("Outer()");
}

Then run the program and you will see Outer is created too. Glad you are interested in how/what's created.