What does this split and trim do?-CodePudding

I'm trying to figure out what this line of code does. I've tried changing it up a little and looked up the regex and can't seem to find any information on what it does to the string.

    public void stringInput(String str) {
        str = str.split("#")[0].trim();
    }

CodePudding user response：

Splits the string into a String[] at every match of regular expression #. Then takes the first String of the array and trim removes the leading and trailing spaces.

CodePudding user response：

Regular expressions consist of characters. Unless that character has a defined special meaning, all characters just mean: Match this character. Thus, the regex "a" would match simply only the string "a" and nothing else.

# has no special meaning.

Therefore, str.split("#") just splits on hash symbols, giving you all the stuff in between them, as array. The [0] part then gets the first entry. So, str.split("#")[0] reduces a string down to 'all characters up to and not including the first # symbol; if the input does not contain one, the entire string'.

Finally, .trim() just lops any spaces off of the start and end.

Note that this is efficiently written but runs slightly inefficiently (it has to make an array with all the parts, and then you toss away all parts but the first), which shouldn't be a problem unless you run this a few hundred thousand times a second. The code as written on its own also does nothing (parameters exist solely within a single method invocation and are tossed in the bin immediately afterwards. So, this updates a local var (str) and then the method ends, meaning that update accomplishes nothing. It would not update anything in what the code that calls this is doing. I assume that's not a problem though - that you just pasted a small part of a much larger method.

CodePudding user response：

This function will remove any texts coming after # and remove any spaces in start or end of text

first part str.split("#")[0] to remove any texts coming after #

example(1) if I have this string:

String str = "Majed#Al-Moqbeli";

the output will be :

Majed

second part trim() to remove any spaces in start or end of text

example(2):

String str = "    MajedAl-Moqbeli    ";

the output will be :

MajedAl-Moqbeli

anther example(3):

 String str = "  Majed  #Al-Moqbeli";

output:

Majed

anther example(4):

 String str = "#MajedAl-Moqbeli";

output well be empty.

note: if I replace # to @ the output well be the same

  public static void main(String[] args) {
    
    String str = "  Majed@Al-Moqbeli";
    stringInput(str);
}

 public static void stringInput(String str) {
    str = str.split("@")[0].trim();
    System.out.println(str);
}