[java] How to remove duplicate white spaces in string using Java?

How to remove duplicate white spaces (including tabs, newlines, spaces, etc...) in a string using Java?

You can use the regex

(\s)\1

and

replace it with $1.

Java code:

str = str.replaceAll("(\\s)\\1","$1");

If the input is "foo\t\tbar " you'll get "foo\tbar " as output
But if the input is "foo\t bar" it will remain unchanged because it does not have any consecutive whitespace characters.

If you treat all the whitespace characters(space, vertical tab, horizontal tab, carriage return, form feed, new line) as space then you can use the following regex to replace any number of consecutive white space with a single space:

str = str.replaceAll("\\s+"," ");

But if you want to replace two consecutive white space with a single space you should do:

str = str.replaceAll("\\s{2}"," ");

Try this - You have to import java.util.regex.*;

    Pattern pattern = Pattern.compile("\\s+");
    Matcher matcher = pattern.matcher(string);
    boolean check = matcher.find();
    String str = matcher.replaceAll(" ");

Where string is your string on which you need to remove duplicate white spaces

Though it is too late, I have found a better solution (that works for me) that will replace all consecutive same type white spaces with one white space of its type. That is:

   Hello!\n\n\nMy    World  

will be

 Hello!\nMy World 

Notice there are still leading and trailing white spaces. So my complete solution is:

str = str.trim().replaceAll("(\\s)+", "$1"));

Here, trim() replaces all leading and trailing white space strings with "". (\\s) is for capturing \\s (that is white spaces such as ' ', '\n', '\t') in group #1. + sign is for matching 1 or more preceding token. So (\\s)+ can be consecutive characters (1 or more) among any single white space characters (' ', '\n' or '\t'). $1 is for replacing the matching strings with the group #1 string (which only contains 1 white space character) of the matching type (that is the single white space character which has matched). The above solution will change like this:

   Hello!\n\n\nMy    World  

will be

Hello!\nMy World

I have not found my above solution here so I have posted it.

You can also try using String Tokeniser, for any space, tab, newline, and all. A simple way is,

String s = "Your Text Here";        
StringTokenizer st = new StringTokenizer( s, " " );
while(st.hasMoreTokens())
{
    System.out.print(st.nextToken());
}

This can be possible in three steps:

1. Convert the string in to character array (ToCharArray)
2. Apply for loop on charater array
3. Then apply string replace function (Replace ("sting you want to replace"," original string"));

If you want to get rid of all leading and trailing extraneous whitespace then you want to do something like this:

// \\A = Start of input boundary
// \\z = End of input boundary 
string = string.replaceAll("\\A\\s+(.*?)\\s+\\z", "$1");

Then you can remove the duplicates using the other strategies listed here:

string = string.replaceAll("\\s+"," ");

hi the fastest (but not prettiest way) i found is

while (cleantext.indexOf("  ") != -1)
  cleantext = StringUtils.replace(cleantext, "  ", " ");

this is running pretty fast on android in opposite to an regex

String str = "   Text    with    multiple    spaces    ";
str = org.apache.commons.lang3.StringUtils.normalizeSpace(str);
// str = "Text with multiple spaces"