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  quick question Doug Mika <dougmmika@gmail.com> - 2013-03-01 10:25 -0800
    Re: quick question Eric Sosman <esosman@comcast-dot-net.invalid> - 2013-03-01 13:48 -0500
      Re: quick question Daniele Futtorovic <da.futt.news@laposte-dot-net.invalid> - 2013-03-01 20:08 +0100
        Re: quick question Donkey Hottie <donkey@fredriksson.dy.fi> - 2013-03-01 22:52 +0200
          Re: quick question Joerg Meier <joergmmeier@arcor.de> - 2013-03-01 22:22 +0100
            Re: quick question Lew <lewbloch@gmail.com> - 2013-03-01 15:31 -0800
    Re: quick question Arne Vajhøj <arne@vajhoej.dk> - 2013-03-01 18:30 -0500
    Re: quick question Roedy Green <see_website@mindprod.com.invalid> - 2013-03-01 15:38 -0800

#22656 — quick question

reading a book a came upon the following inside a 'myDialog extends JDialog" class inside an actionlistener implemented as an anonymous inner class.

myDialog.this.dispose()

why not simply write

this.dispose()

does it have anything do with the fact that this line is found within an anonymous inner class that is an actionListener?

Thanks
Mika

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#22657

On 3/1/2013 1:25 PM, Doug Mika wrote:
> reading a book a came upon the following inside a 'myDialog extends JDialog" class inside an actionlistener implemented as an anonymous inner class.
>
> myDialog.this.dispose()
>
> why not simply write
>
> this.dispose()

     That would be perfectly all right, if you get your thrills
from reading the compiler's error messages.  :)

> does it have anything do with the fact that this line is found within an anonymous inner class that is an actionListener?

     Yes.  An unadorned `this' would refer to the instance of the
class whose code is running.  That's the anonymous class that
implements ActionListener, a class that doesn't even *have* a
dispose() method (unless one's been added explicitly in the
anonymous class, which would be awfully strange).

     Writing `this.dispose()' or simply `dispose()' would try
to call the anonymous class' dispose() method, not any method
belonging to the enclosing myDialog (poor choice of name, BTW).
The intent, most likely, is to close the dialog -- so the code
uses `myDialog.this' to mean "Not *this* `this', but the `this'
of the enclosing class named `myDialog'."  It's that enclosing
class' dispose() that's being called.

-- 
Eric Sosman
esosman@comcast-dot-net.invalid

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#22658

On 01/03/2013 19:48, Eric Sosman allegedly wrote:
> On 3/1/2013 1:25 PM, Doug Mika wrote:
>> reading a book a came upon the following inside a 'myDialog extends
>> JDialog" class inside an actionlistener implemented as an anonymous
>> inner class.
>>
>> myDialog.this.dispose()
>>
>> why not simply write
>>
>> this.dispose()
> 
>     That would be perfectly all right, if you get your thrills
> from reading the compiler's error messages.  :)
> 
>> does it have anything do with the fact that this line is found within
>> an anonymous inner class that is an actionListener?
> 
>     Yes.  An unadorned `this' would refer to the instance of the
> class whose code is running.  That's the anonymous class that
> implements ActionListener, a class that doesn't even *have* a
> dispose() method (unless one's been added explicitly in the
> anonymous class, which would be awfully strange).
> 
>     Writing `this.dispose()' or simply `dispose()' would try
> to call the anonymous class' dispose() method, not any method
> belonging to the enclosing myDialog (poor choice of name, BTW).
> The intent, most likely, is to close the dialog -- so the code
> uses `myDialog.this' to mean "Not *this* `this', but the `this'
> of the enclosing class named `myDialog'."  It's that enclosing
> class' dispose() that's being called.
> 

For the record, it's called a "Qualified 'this'", and the specification
can be found here:
<http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.8.4>

-- 
DF.

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#22662

01.03.2013 21:08, Daniele Futtorovic kirjoitti:
> On 01/03/2013 19:48, Eric Sosman allegedly wrote:
>> On 3/1/2013 1:25 PM, Doug Mika wrote:
>>> reading a book a came upon the following inside a 'myDialog extends
>>> JDialog" class inside an actionlistener implemented as an anonymous
>>> inner class.
>>>
>>> myDialog.this.dispose()
>>>
>>> why not simply write
>>>
>>> this.dispose()
>>
>>     That would be perfectly all right, if you get your thrills
>> from reading the compiler's error messages.  :)
>>
>>> does it have anything do with the fact that this line is found within
>>> an anonymous inner class that is an actionListener?
>>
>>     Yes.  An unadorned `this' would refer to the instance of the
>> class whose code is running.  That's the anonymous class that
>> implements ActionListener, a class that doesn't even *have* a
>> dispose() method (unless one's been added explicitly in the
>> anonymous class, which would be awfully strange).
>>
>>     Writing `this.dispose()' or simply `dispose()' would try
>> to call the anonymous class' dispose() method, not any method
>> belonging to the enclosing myDialog (poor choice of name, BTW).
>> The intent, most likely, is to close the dialog -- so the code
>> uses `myDialog.this' to mean "Not *this* `this', but the `this'
>> of the enclosing class named `myDialog'."  It's that enclosing
>> class' dispose() that's being called.
>>
> 
> For the record, it's called a "Qualified 'this'", and the specification
> can be found here:
> <http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.8.4>
> 

This "Qualified this" is kind of hard to understand. How

    myDialog.this.dispose()

differs from

    myDialog.dispose()

If myDialog is an object instance, would't it be sufficient just call
dispose it?



-- 

"Unfortunately suspend does mean things sometimes"

Husse Apr 25 2007

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#22663

On Fri, 01 Mar 2013 22:52:42 +0200, Donkey Hottie wrote:

> This "Qualified this" is kind of hard to understand. How

>     myDialog.this.dispose()

> differs from

>     myDialog.dispose()

> If myDialog is an object instance, would't it be sufficient just call
> dispose it?

Despite the ill chosen name, myDialog is a class name, not an object
instance:

> 01.03.2013 21:08, Daniele Futtorovic kirjoitti:
>> On 01/03/2013 19:48, Eric Sosman allegedly wrote:
>>> On 3/1/2013 1:25 PM, Doug Mika wrote:
>>>> reading a book a came upon the following inside a 'myDialog extends
>>>> JDialog" class

Liebe Gruesse,
		Joerg

-- 
Ich lese meine Emails nicht, replies to Email bleiben also leider
ungelesen.

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#22666

Joerg Meier wrote:
> Donkey Hottie wrote:
>> This "Qualified this" is kind of hard to understand. How
>>     myDialog.this.dispose()
>> differs from
>>     myDialog.dispose()
> 
>> If myDialog is an object instance [sic], would't it be sufficient just [to] call
>> dispose [on] it?

If it were an instance reference, it wouldn't be the enclosing instance.

> Despite the ill chosen name, myDialog is a class name, not an object
> instance:

-- 
Lew

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#22665

On 3/1/2013 1:25 PM, Doug Mika wrote:
> reading a book a came upon the following inside a 'myDialog extends
> JDialog" class inside an actionlistener implemented as an anonymous
> inner class.
>
> myDialog.this.dispose()
>
> why not simply write
>
> this.dispose()
>
> does it have anything do with the fact that this line is found within
> an anonymous inner class that is an actionListener?

Other have already explained the difference between the two lines.

Two examples to supplement:

ThisFun1:

public class ThisFun1 {
	public static void main(String[] args) {
		A a = new A();
		A.B b = a.new B();
		A.B.C c = b.new C();
		c.demo();
	}
}

class A {
	public void dump() {
		System.out.println("I am A");
	}
	class B {
		public void dump() {
			System.out.println("I am B");
		}
		class C {
			public void dump() {
				System.out.println("I am C");
			}
			public void demo() {
				dump();
				this.dump();
				C.this.dump();
				B.this.dump();
				A.this.dump();
			}
		}
	}
}

ThisFun2:

public class ThisFun2 {
	public static void main(String[] args) {
		X x = new X();
		x.demo();
	}
}

class X {
	public void dump() {
		System.out.println("I am X");
	}
	public void demo() {
		call(new Y() {
			public void m() {
				dump();
				this.dump();
				X.this.dump();
			}
		});
	}
	public void call(Y y) {
		y.m();
	}
}

abstract class Y {
	public abstract void m();
	public void dump() {
		System.out.println("I am Y");
	}
}

Arne

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#22669

On Fri, 1 Mar 2013 10:25:18 -0800 (PST), Doug Mika
<dougmmika@gmail.com> wrote, quoted or indirectly quoted someone who
said :

>does it have anything do with the fact that this line 
>is found within an anonymous inner class that is an actionListener?

Inside the anonymous class "this" refers to the  dependent anonymous
class  object.  by prefixing the class you get the outer object.
-- 
Roedy Green Canadian Mind Products http://mindprod.com
One thing I love about having a website, is that when I complain about
something, I only have to do it once. It saves me endless hours of 
grumbling.

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