CODEWITHSUNDEEP
javastringsplitconcatenation
leyla moazami
leyla moazami

Reputation: 267

How to concatenate several strings with different format and then split them


Hi all.
I want to concatenate some strings without specified format in java. for example I want to concatenate multiple objects like signature and BigInteger and string, that all of them are converted to string. So i can not use of the specified delimiter because each delimiter may be exist in these strings. how i can concatenate these strings and then split them?
thanks all.

Upvotes: 1

Views: 2894

Answers (3)

GuruKulki
GuruKulki

Reputation: 26428

You concatenate using the concatenation operator(+) as below:

String str1 = "str1";
String str2 = "str2";
int inte = 2;

String result = str1+str2+inte;

But to split them back again you need some special character as delimiter as the split function in String works on delimiter.

Upvotes: 0

corsiKa
corsiKa

Reputation: 82589

You can escape the delimiter in your string. For example, let's say you have the following strings:

String a = "abc;def";
String b = "12345:";
String c = "99;red:balloons";

You want to be able to do something like this

String concat = a + delim + b + delim + c;
String[] tokens = concat.split(delim);

But if our delim is ";" then quite clearly this will not suffice, as we will have 5 tokens, and not 3. We could use a set of possible delimiters, search the strings for those delimiters, and then use the first one that isn't in the target strings, but this has two problems. First, how do we know which delimiter was used? Second, what if all delimiters exist in the strings? That's not a valid solution, and it's certainly not robust.

We can get around this by using an escape delimiter. Let us use ":" as our escape delimiter. We can use it to say "The next character is just a regular old character, it doesn't mean anything important."

So if we did this:

String aEscaped = a.replace(";",":;");
String bEscaped = b.replace(";",":;");
String cEscaped = c.replace(";",":;");

Then, we can split the concat'd string like

String tokens = concat.split("[^:];")

But there is one problem: What if our text actually contains ":;" or ends with ":"? Either way, these will produce false positives. In this case, we must also escape our escape character. It basically says the same thing as before: "The next character does nothing special."

So now our escaped strings become:

// note we escape our escape token first, otherwise we'll escape 
// real usages of the token
String aEscaped = a.replace(":","::").replace(";",":;");
String bEscaped = b.replace(":","::").replace(";",":;");
String cEscaped = c.replace(":","::").replace(";",":;");

And now, we must account for this in the regex. If someone knows a regex that works for this, they can feel free to edit it in. What occurs to me is something like concat.split("(::;|[^:];)") but it doesn't seem to get the job done. The job of parsing it would be pretty easy. I threw together a small test driver for it, and it seems to work just fine.

Code found at http://ideone.com/wUlyz

Result:

abc;def becomes abc:;def
ja:3fr becomes ja::3fr
; becomes :;
 becomes 
: becomes ::
83;:;:;;;; becomes 83:;:::;:::;:;:;:;
:; becomes :::;
Final product:
abc:;def;ja::3fr;:;;;::;83:;:::;:::;:;:;:;;:::;
Expected 'abc;def', Actual 'abc;def', Matches true
Expected 'ja:3fr', Actual 'ja:3fr', Matches true
Expected ';', Actual ';', Matches true
Expected '', Actual '', Matches true
Expected ':', Actual ':', Matches true
Expected '83;:;:;;;;', Actual '83;:;:;;;;', Matches true
Expected ':;', Actual ':;', Matches true

Upvotes: 2

JB Nizet
JB Nizet

Reputation: 691933

Use a well-defined format, like XML or JSON. Or choose a delimiter and escape every instance of this delimiter in each of the Strings. Or prepend the length of each part in the message. For example:

10/7/14-<10 chars of signature><7 chars of BigInteger><14 chars of string>

or

10-<10 chars of signature>7-<7 chars of BigInteger>14-<14 chars of string>

Upvotes: 3

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