Inner Classes and the word 'this'- Chapter 8 Question 9 page 697

[Glen Iris]

public class Car{
	class Engine{
	 //insert code here
	}
	public static void main(String args[]){
		new Car().go();
	}
	void go(){
		new Engine();
	}
	void drive(){System.out.println("hi");}
} 

Hello once again friends.

I understand that to reference the outer class from within an inner class the syntax is OuterClassName.this and therefore I can see that if

Car.this.drive();

were placed on line 3 that the output would be "hi".

However, I am still confused about two things -

1 - I cannot understand why Car.this.drive(); needs to be wrapped in chain brackets, ie

{Car.this.drive();}

2 - Placing the code

Engine() {Car.this.drive()};

will produce the same output (hi). How is this so? Is this line of code effectivley saying to the JVM - "Regarding your Engine instance, call Car.this.drive()"?

[Anayonkar Shivalkar]

Glen Iris wrote: 1 - I cannot understand why Car.this.drive(); needs to be wrapped in chain brackets

That is because, method invocation is not allowed inside a class and outside any method and any initializing block.
When we say

class Engine{
	 {Car.this.drive();}
	}

then we put method call to drive inside initialization block, hence it works.

Glen Iris wrote: 2 - Placing the code

Engine() {Car.this.drive()};

will produce the same output (hi). How is this so?

Well, that is because, the call to drive method was simply removed from initializer block and added to default constructor of Engine. When go method creates a new object of Engine, drive method is invoked.

I hope this helps.

[Glen Iris]

Thank you Anayonkar Shivalkar. Your explaination is very clear and i now understand the solutions. :-)

[prashant modak]

when you compile the code:

class A
{
System.out.println("hello");
}
class B
{
public static void main(String [] args)
{
A a=new A();
}
}

You will get an error.......
But if you put System.out.println("hello"); inside parenthesis you wont get any error......
cause when you put that statement inside parenthesis then it become an init block...which get loaded in stack
when we instantiate A.
so Parenthesis are required..........