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Question On Nesting A Class Within A Method

4 replies on 1 page. Most recent reply: Mar 9, 2004 8:50 AM by twc

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Kevin

Posts: 25
Nickname: doublek321
Registered: Jan, 2004

Question On Nesting A Class Within A Method Posted: Mar 8, 2004 9:21 PM
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My question relates to the code below.

First off, what is the proper way to refer to the class "NestedClass"? Is it a local inner class? Is it "inner" because it is within another class and "local" because it falls out of scope at all times other than when inside the method?

Secondly (and I think I know the answer to this but want confirmation), is there any way to call the method "anotherWayToPrintPrivString"? I would guess the answer is "no" because I'm thinking you'd have to downcast to call it like this...

((NestedClass)mi).printIt();


Is the reason you can't downcast this because of the "local" part of "local inner class"?


interface MyInterface {
	void printPrivString();
}
 
 
class NestClassWithinMethod {
	MyInterface methodWithNestedClass (String theString) {
		class NestedClass implements MyInterface {
			private String privString;
 
			NestedClass(String abc) {
				privString = abc;
			}
			
			public void printPrivString() {
				System.out.println("NestedClass.printPrivString privString is " + privString);
			}
			
			public void anotherWayToPrintPrivString() {
				System.out.println("privString = " + privString);
			}
		}
		
		return new NestedClass(theString);
	}
	
	public static void main (String args[]) {
		NestClassWithinMethod ncwm = new NestClassWithinMethod();
		MyInterface mi = ncwm.methodWithNestedClass("how now brown cow");
		mi.printPrivString();
		//((NestedClass)mi).printIt();
	}
}
 


Kevin

Posts: 25
Nickname: doublek321
Registered: Jan, 2004

Re: Question On Nesting A Class Within A Method Posted: Mar 8, 2004 9:26 PM
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> Secondly (and I think I know the answer to this but want
> confirmation), is there any way to call the method
> "anotherWayToPrintPrivString"?


Actually the end of the question should read...

is there any way to call the method "anotherWayToPrintPrivString" from main?

twc

Posts: 129
Nickname: twc
Registered: Feb, 2004

Re: Question On Nesting A Class Within A Method Posted: Mar 8, 2004 11:47 PM
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Not without casting. This goes back to what I was explaining about interfaces in one of the other posts. Since you have mi declared as a MyInterface object, the compiler only "knows" about the printPrivString() method since that is the only one guaranteed to be there by the interface.

If you either declare it or typecast it to a NestedClass object, then the compiler can read the NestedClass file to see what other methods a NestedClass object contains. (Disclaimer: I've never seen a class declared in a method like this, so I don't even know if you *can* declare or typecast it.)

twc

Kevin

Posts: 25
Nickname: doublek321
Registered: Jan, 2004

Re: Question On Nesting A Class Within A Method Posted: Mar 9, 2004 12:08 AM
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> If you either declare it or typecast it to a NestedClass
> object, then the compiler can read the NestedClass file to
> see what other methods a NestedClass object contains.

I'm wondering if there is any way to downcast it though. The class is defined ONLY within the method.

twc

Posts: 129
Nickname: twc
Registered: Feb, 2004

Re: Question On Nesting A Class Within A Method Posted: Mar 9, 2004 8:50 AM
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> > If you either declare it or typecast it to a
> NestedClass
> > object, then the compiler can read the NestedClass file
> to
> > see what other methods a NestedClass object contains.
>
> I'm wondering if there is any way to downcast it though.
> The class is defined ONLY within the method.

Try it. As I said before, I've never seen code done like this, so you're getting out of my league. Sorry.
twc

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