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How to compare and sort two differenent strings. (Read 1051 times)

danielt

How to compare and sort two differenent strings.
Dec 21^st, 2009, 5:15am

Hi There.

So, if I have a string such as:
Code:


String num = "1233445.023";

Is there a simple way to check if the String has a "." in it?

I am writing a simple calculator and want to make sure the user can only enter a maximum of one "." when typing in the numbers.

the only idea I have is to use toCharArray() and then loop through it each time it's updated with the substring method to see if it has more than one "." in it.

My intuition tells me I'm over-complicating things. Any other suggestions??

Thanks,

Dan.

sojamo

Re: How to compare and sort two differenent strings.
Reply #1 - Dec 21^st, 2009, 6:14am

you can use indexOf to check if a particular substring is contained inside a String. in your case the "."

Code:


String num = "1233445.023"; 
println(num.indexOf(".")); // prints 7

here num.indexOf(".") will return 7 - the index of the substring you have been looking for. if a string does not contain the substring you are looking for, -1 will be returned.
Code:


String num = "1233445"; 
println(num.indexOf(".")); // prints -1

andreas schlegel / http://www.sojamo.de

Cedric YaBB Moderator Offline Posts: 1838	Re: How to compare and sort two differenent strings. Reply #2 - Dec 21^st, 2009, 6:19am as you want to check if you have one or more. you then have to create a substring from this position and check if it still contains a "."
	twitter.com/CedricKiefer

JR Full Member Offline Posts: 149	Re: How to compare and sort two differenent strings. Reply #3 - Dec 21^st, 2009, 6:44am This should do the trick: Code: boolean containsAtMostOneDot(String s) { return s.indexOf(".") == s.lastIndexOf("."); }

blindfish

Re: How to compare and sort two differenent strings.
Reply #4 - Dec 21^st, 2009, 6:48am

You only want to check if you already have single point in the string (no need to check for more) - and then simply not allow another point to be added if there is (though I think that's what you meant in the first place).

So assuming your numbers are being stored in a string buffer* as they're added (i.e. until an operator is selected), simply check for the presence of a decimal point in this buffer when they hit the '.' button (see Reference > String Functions > maybe 'match()'?). If there's already one there don't add another point to the buffer.

That's how I would do it anyway...

* e.g. something like this rather than an array:
String foo;
foo += inputString;

IIRC as long as 'inputString' is indeed a string it should be concatenated to the existing string...

Where is the what if the what is in why?

danielt

Re: How to compare and sort two differenent strings.
Reply #5 - Dec 21^st, 2009, 8:04pm

Thanks for the speedy resonse guys!

Both examples are far more effecient than what I had in mind. match() sounds ideal except for one problem I found with it.

In my case I am seaching for "."

here's and example using match()
Code:


String s1 = "12394802";

String[] m1 = match(s1, ".");
if (m1 != null) {
  // This will print to the console.
  println("Found a match in '" + s1 + "'");  
} else {
  println("No match found in '" + s1 + "'");
}

the problem is that "." seems to be some sort of special search character. According to this http://java.sun.com/j2se/1.4.2/docs/api/java/util/regex/Pattern.html it means "Any Character" Sad

I'm out of my depth here when it comes to expressions and java.

I think I will go with sojamo's example unless anyone can suggest a way to force match() to see "." as a regular character?

Thanks again guys,

You are always very helpful.

Dan.

Re: How to compare and sort two differenent strings.
Reply #6 - Dec 21^st, 2009, 10:37pm

If you are trying to see if there is a dot present, match() is overkill. I recommend using the code I posted above or another variant using indexOf.

But to answer the question, you have to escape the dot: match(s1, "\\.");

Edit:
I've just done a small speed test, if you don't need other functionality from match (regexes, grouping, ...) you really should use indexOf, it's roughly 35 times faster (depending on the input of course)

danielt YaBB Newbies Offline Posts: 36 South Australia	Re: How to compare and sort two differenent strings. Reply #7 - Dec 21^st, 2009, 10:55pm Great thanks JR, I have been using indexOf and it does the trick. Thanks for doing the speed test too! Dan.

danielt YaBB Newbies Offline Posts: 36 South Australia	Re: How to compare and sort two differenent strings. Reply #8 - Dec 22^nd, 2009, 12:53am FYI here's what I'm working on: http://www.openprocessing.org/visuals/?visualID=6650 Cheers!

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