Replace extra spaces in string with a single space in Java, without regex

Question

I want to basically to do this:

String secondString = firstString.trim().replaceAll(" +", " ");

Or replace all the multiple spaces in my string, with just a single space. However, is it possibly to do this without regex like I am doing here?

Thanks!

Java has a replace() method for strings that will find a given string and replace it with another string. Generally, we expect you to at least make a try at programming something before asking a question . . . then we will make suggestions from there. — Frank Merrow
– Frank Merrow, Commented Feb 15, 2020 at 19:44

Elliott Frisch · Accepted Answer · 2020-02-15 19:35:58Z

1

However, is it possibly to do this without regex like I am doing here?

Yes. The regular expression is clear and easy to read, so I would probably use that; but you could use a nested loop, a StringBuilder and Character.isWhitespace(char) like

StringBuilder sb = new StringBuilder();
for (int i = 0; i < firstString.length(); i++) {
    sb.append(firstString.charAt(i));
    if (Character.isWhitespace(firstString.charAt(i))) {
        // The current character is white space, skip characters until 
        // the next character is not.
        while (i + 1 < firstString.length() 
                    && Character.isWhitespace(firstString.charAt(i + 1))) {
            i++;
        }
    }
}
String secondString = sb.toString();

Note: This is a rare example of a nested loop that is O(N); the inner loop modifies the same counter as the outer loop.

edited Feb 15, 2020 at 19:35

answered Feb 15, 2020 at 19:29

Elliott Frisch

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