Java: Replacing Multiple Spaces with Single Space and Trimming Leading and Trailing Spaces

To address the task of reducing multiple spaces to a single space and eliminating leading and trailing spaces, we have several Java solutions.

Solution 1: Using trim() and replaceAll()

This solution utilizes the trim() method to remove the leading and trailing spaces, followed by replaceAll() to combine multiple spaces into a single space:

String after = before.trim().replaceAll("  ", " ");

Solution 2: Regex-only

While less readable, it's feasible to resolve the problem with a single replaceAll() utilizing a complex regular expression:

String[] tests = {
  "  x  ",      
  "  1   2   3  ",  
  "",             
  "   ",          
};
for (String test : tests) {
  System.out.format("[%s]%n",
      test.replaceAll("^  |  $|( ) ", "$1")
  );
}

Solution Details

• Solution 1: trim() removes all leading and trailing whitespace, while replaceAll() replaces consecutive spaces with a single space.
• Solution 2: The regex achieves the same result in a single step. It matches and replaces sequences of spaces at the beginning, end, or middle of the string with either an empty string (to remove extra spaces) or a single captured space (to keep single spaces intact).

Additional Resources

• [String.trim() documentation](https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#trim--)
• [Regular expression repetition patterns](https://www.regular-expressions.info/Repetition)
• [Regular expression anchors](https://www.regular-expressions.info/Anchors)