ColdFusion String Comparison: Compare() vs. Equals() vs. CompareTo()

Posted September 5, 2006 at 1:12 PM by Ben Nadel

Tags: ColdFusion

Reader Comments

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Cool man thanks for taking the time to do this - I am in a project where I'm going to be manipulating strings from a db based on replace rules and I need to do a comparison once the manipulation/rules have been run on the database strings - then if the values are not the same as the origional, then I update the updated string to the db -
I was debating on what function to use and was leaning towards compare() as it was - this solidified it!

I just stumbled across this though google and thought I'd shed some light on it. The reason the CF method is faster is because when you call a Java method in CF it uses reflection to call the method... which is quite expensive.

In fact, what CF really does is call java.lang.Class#getMethods() [1], do a search through the result to find a matching name and then try and match up the types of the arguments. It does cache the match result so subsequent calls are faster, but there's definitely overhead from doing a method call like this.

On the other hand CF's Compare function might look like this in Java:

public int Compare( String a, String b ) {
int r = a.compareTo( b );
if( r > 0 ) return 1;
return r == 0 ? 0 : -1;
}

So it should definitely be faster than doing a lookup for the method.

Things have gotten a lot faster over the years though in the Java world... [2]. :) Shame there's such a horrible class loader issue in Java 1.6 :/

[1] http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Class.html#getMethods()
[2] http://www.jguru.com/faq/view.jsp?EID=246569

@Elliott,

Thanks for the insight. Yeah, I have read a few really bad things about the Class Loader in Java 1.6. It seems like with CF8, a lot of people are going with Java 1.5. At least, that's what I think I've read.

Ben,

Is there a way in Coldfusion to do a SQL like comparison?

For example, I have a webform that has a ID drop down - the iD looks something like this "AC1200" or "PR1982" etc.

Now what i wanna do is look at the first 2 characters of the ID, and based on that, enter a certain value in a column in the DB. SO that every time a "AC" appears in the ID, I should enter a specific value. Similarly, for each "PR..." entry, I want another value.

I know we can do a "WHERE Var LIKE AC%" comparison in SQL, but not totally sure if and/or how that can be done in CF!

@UMTerp,

You can use REFind() for this:

<cfif REFind( "^AC", variable )> ... </cfif>

The RE = "regular expression". The "^" signifies the beginning of the string. So ^AC matches "AC" as the first part of the string.

You can also use the Left() function to get the first 2 characters of the term - even trim it first then use Left(string,count).

@Ben Nadel,

Great, it worked!! You got unbelievable reply speed! - within 6 mins of my query!!

Thanks!

@UMTerp,

Ha ha, glad to help.

@Kevin,

Using left is good also.

This is why I hate coldfusion. It doesn't hold to any conventions about how objects should be compared. For example, strings of different lengths get evaluated completely differently. I know of no other language that does this.

<cfscript>
a = '12345';
b = '12346';
// Should be false, and is false.
writeoutput('a eq b == #a eq b#<br />');

a = '2707200116272368271111';
b = '2707200116272368279465';
// Should be false, but isn't.
writeoutput('a eq b == #a eq b#<br />');
</cfscript>

@Chris, Ben and others,

Re. Chris's comment about the difference in comparison results, could anyone explain why that is happening?

@UMTerp,

My guess is that the strings that @Chris is comparing in the latter example are being converted to numbers for the comparison and the numbers that large cannot be compared well. As such, they get truncated and their truncations happen to be equal.

If you change the strings to have a preceeding, non-numeric value:

a = '_2707200116272368271111';
b = '_2707200116272368279465';

... then they are NOT equal. So, something is happen when it tries to convert them to numbers.

I've personally never had to deal with numbers this large, so it's never caused a problem. But, if you don't know why its happening, you can pull your hair out trying to debug this!

@UMTerp,

Incidentally, if you use the Compare() function, this works with strings explicitly:

#NOT Compare( a, b )# == NO

.. which is what we expect.

The most recent part of this discussion was also carried on over in the Railo group. Figure I would post a link for those interested.

http://groups.google.com/group/railo/browse_thread/thread/2b326e81c8e5e399?hl=en

Besides speed there is something to consider when choosing a comparison method:

Today I spend hours to find a "bug" in the simple statement

// if (left (tf, j) is curr_dp) { ....
if (compare (left (tf, j), curr_dp) is 0) { ....

the simple test "is" fooled me for hours ... given these values:

curr_dp is "+43", left (tf, j) is "043"

Both are strings, curr_dp comes from a query

curr_dp = Prefix_Query["DIAL_PREFIX"][i];

and

tf is a phone number like "0431234567"

When using the if statemet with "is", it always returned true. It took me hours because I never thought of such a behavior, because both are strings (at least in my mind). Obviously one CAN see them as numerics, which makes them match.

I will never use "is" again ... :-)

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