Split space from string not working in Kotlin

问题

Anyone wonder this ? Splitting SPACE (" ") in kotlin is not working, i tried with different regex codes but is not working at all.

Tried with this :

value.split("\\s")[0];
value.split("\\s+")[0];
value.split("\\s++")[0];

Then i came up with solution -> Create java constant class which contains this function and returns string array to your kotlin class.

Is there any other solution for this problem where we can directly achieve this thing?

Solution : As @Edson Menegatti said :

KOTLIN Specific : WORKING

values.split("\\s".toRegex())[0]

Many people suggested this solution : NOT WORKING

values.split(" ")[0] 

But in my case it's not working.

回答1:

Here's an issue between the Java and Kotlin implementation of String.split.

While the Java implementation does accept a regex string, the Kotlin one does not. For it to work, you need to provide an actual Regex object.

To do so, you would update your code as follows:

value.split("\\s".toRegex())[0];

Also, as @Thomas suggested, you can just use the regular space character to split your string with:

value.split(" ")[0];

Final point, if you're only using the first element of the split list, you might want to consider using first() instead of [0] - for better readability - and setting the limit parameter to 2 - for better performance.

回答2:

You need to use :

.toRegex()

fun main(args: Array<String>) {
        val str = "Kotlin com"

        val separate1 = str.split("\\s".toRegex())[0]
        println(separate1) // ------------------> Kotlin
}

OR

You can also use .split(" ")[0] to achieve result. Like

fun main(args: Array<String>) {
            val str = "Kotlin com"

            val separate1 = str.split(" ")[0]
            println(separate1) // ----------> Kotlin
}

回答3:

String#split (actually CharSequence#split) can take either a regular expression, or just a string which is interpreted literally. So:

value.split(" ")[0]

does what you want.

If you're only using the first element, it's more efficient to also pass limit = 2. Or, even better, use substringBefore.

回答4:

Kotlin tries to resolve some issues that Java's String library has. For instance, Kotlin tries to be more explicit.

As a result, the split method takes a normal String and does not use it as a regex internally:

"hello world".split("\\s")[0] //no match
"hello world".split(" ")[0] // => "hello"

To explicitly use the overloaded split function that actually takes a regex, the toRegex() extension can be used (inline fun String.toRegex(): Regex (source)):

"hello world".split("\\s".toRegex())[0]// => "hello"

The following shows another example of Kotlin resolving the confusing String::replaceAll method:

Taken from a KotlinConf presentation of Svetlana Isakova, co-author of “Kotlin in Action”

来源：https://stackoverflow.com/questions/48379981/split-space-from-string-not-working-in-kotlin