Inner-class Confusion

[Arhaan Singhania]

Hello,
This is a code from javachamps about inner-classes.

public class AirJet {

	public static void main(String[] args) {
		
		// instantiation 1
		Engine engine1 = new AirJet().new Engine();
		
		// instantiation 2
		AirJet.Engine engine2 = new AirJet().new Engine();
		
		// instantiation 3
		AirJet airjet = new AirJet();
		Engine engine3 = airjet.new Engine();

		// instantiation 4
		Engine engine4 = new Engine();
		
	}
	
	class Engine{
		
	}
}

It asked about which instantiations are correct. But in instantiation 1 and 3, can we qualify an inner class without its
outer-class name. I am confused. Please help.

Arhaan

[Stephan van Hulst]

What happened when you ran the code?

[Arhaan Singhania]

Hello Stephan,
It worked well for the first three instantiations. I was just wondering. Ofcourse compiler allows it means we can do that.
But i was just asking, how come Engine is allowed without its parent name.
Arhaan

[Pramod P Deore]

In first and second instantiation you had used new new AirJet().new Engine();

// instantiation 1
		Engine engine1 = new AirJet().new Engine();
		
		// instantiation 2
		AirJet.Engine engine2 = new AirJet().new Engine();

and in third instantiation you had first created object of Airjet and using that object you instantiated as

// instantiation 3
		AirJet airjet = new AirJet();
		Engine engine3 = airjet.new Engine();

So here is also works.

[Pramod P Deore]

And one more thing:

Engine engine1 = new AirJet().new Engine();

and

AirJet airjet = new AirJet();
Engine engine1 = airjet.new Engine();

are equivalent.

[Stephan van Hulst]

Arhaan Singhania wrote:Hello Stephan,
It worked well for the first three instantiations. I was just wondering. Ofcourse compiler allows it means we can do that.
But i was just asking, how come Engine is allowed without its parent name.
Arhaan

Because of the scope. You are using the Engine identifier from the main method inside the AirJet class. Since the scope is already inside AirJet, it assumes you are referring to the inner class Engine. You would not be able to do this if you used Engine outside the AirJet class, then you would have to use AirJet.Engine instead.

[Arhaan Singhania]

Hello Stephen/Pramod,

Thankyou very much. I have understood the concept very well and Stephen the scoping explanation was awesome.
Thanks a ton.

Arhaan