instanceof ..?

mohama · 01-11-2006, 05:15 PM

hi,

i have a question ?
how can i know with which constructor a specific object was created .. i mean which constructor within the class(in case there are more than one ) had initialise the object i have ??

-- i do know that the object i have is instaceof class X for example , but what i ask is within class X which constructor built it .. ?
-- i am using java ..!

muhammad-sameer,

graemef · 01-11-2006, 05:30 PM

I don't know of a way to find that out unless you put the clue in the constructor itself, that is you have a property which each constructor would set to different values.

graeme.

mohama · 01-11-2006, 05:35 PM

well , this is exactly the problem i face , since i use doubles , and using '==' is problematic , and the EPSILON to use inorder to determine wither two doubles are equals : |d1-d2|<EPSILON
is the parameter i initialise at the constructor ...

thanks ,
m-s

vivekr · 01-11-2006, 06:48 PM

Can u post the constructor codes?

mohama · 01-11-2006, 07:04 PM

it's simple code ... but in order to implement the equals () method ( it's defined true iff the two objects were created by the same constructor with the same _precision)

Code:

public SineFunction ( )
{
     this( EPSILON ) ;
}

Code:

public SineFunction ( double precision )
{
     _precision = precision ;
}

the point is that i can't check wether ... |EPSILON - EPSILON|<EPSILON ..???!!!

hope that it's clearer now , thanks alot ,
m-s

xhi · 01-11-2006, 11:55 PM

Quote:

the point is that i can't check wether ... |EPSILON - EPSILON|<EPSILON ..???!!!

hope that it's clearer now , thanks alot ,
m-s

graeme has a good point... the approach i also would take would be to put a flagg in the class.. i do not know of any other way to find out which constructor was called after the control has returned from the constructor.. though i am no java expert, but i still dont see this being possible.. here is a rough idea..

Code:

private boolean precisionSet;
public SineFunction ( ){
     precisionSet=false;
     this( EPSILON ) ;
}
public SineFunction ( double precision ){
     precisionSet=true;
     _precision = precision ;
}

then when you overload the operators you can put in code to test for the precision and do any conversions or whatnot on the fly..

hth

<edit>fixed broken quote!</edit>

graemef · 01-12-2006, 07:09 AM

Quote:

the point is that i can't check whether ... |EPSILON - EPSILON|<EPSILON ..???!!!

I think you want.

Code:

|d1-d2|<EPSILON

where d1 and d2 are objects of double.

If EPSILON is always a fixed value then I would make it static so that you have the same value for every instance of double. If not then you will need to make a decision on which EPSILON to use, I would guess that the double to the left of the operation would make sense, hence

Code:

double d1(56.5, 0.5);
double d2(56.0, 0.25);
...
d1.equal(d2); // would use EPSILON .5 and equate to true
d2.equal(d1); // would use EPSILON .25 and equate to false

I hope that helps a little.

graeme.

vivekr · 01-12-2006, 10:57 AM

Can u exaplain ur code graeme...
I wonder what the two argument constructor does...

graemef · 01-12-2006, 11:25 AM

Well the idea was that the first argument was the actual value whilst the second argument was the epsilon value. This only necessary if the epsilon value may change and it could be defaulted to a fixed value. Also the actual values I used are not very good ones! You would want the epsilon to be much smaller in relation to the magnitude of the actual number.

graeme