How to trim the whitespace from a string? [duplicate]

Answer 1

You can use Guava CharMatcher.

String outputString = CharMatcher.whitespace().trimFrom(inputString);

Note: This works because whitespace is all in the BMP.

Answer 2

First of all, what others said about String.trim(). Really, don't reinvent the wheel.

But for the record, what's going wrong with your code is that Java arrays aren't resizeable. When you initially set up your target array, you create it as a size 0 array. You then tell System.arraycopy to stuff len - 1 characters in there. That's not going to work. If you wanted it to work, you'd need to set up the array as:

char[] newChars = new char[len - 1];

But that's amazingly inefficient, reallocating and copying a new array each time through the loop. Use the three steps that Stephen C mentioned, ending with a substring.

Answer 3

With JDK/11, now you can make use of the String.strip API to return a string whose value is this string, with all leading and trailing whitespace removed. The javadoc for the same is :

/**
 * Returns a string whose value is this string, with all leading
 * and trailing {@link Character#isWhitespace(int) white space}
 * removed.
 * <p>
 * If this {@code String} object represents an empty string,
 * or if all code points in this string are
 * {@link Character#isWhitespace(int) white space}, then an empty string
 * is returned.
 * <p>
 * Otherwise, returns a substring of this string beginning with the first
 * code point that is not a {@link Character#isWhitespace(int) white space}
 * up to and including the last code point that is not a
 * {@link Character#isWhitespace(int) white space}.
 * <p>
 * This method may be used to strip
 * {@link Character#isWhitespace(int) white space} from
 * the beginning and end of a string.
 *
 * @return  a string whose value is this string, with all leading
 *          and trailing white space removed
 *
 * @see Character#isWhitespace(int)
 *
 * @since 11
 */
public String strip()

The sample cases for these could be:--

System.out.println("".strip());
System.out.println("  both  ".strip());
System.out.println("  leading".strip());
System.out.println("trailing  ".strip());

Answer 4

The simple way to trim leading and trailing whitespace is to call String.trim(). With Java 11 and later, you can also use String.strip() which uses a different interpretation of what "white space" means¹.

If you just want to trim just leading and trailing spaces (rather than all leading and trailing whitespace), there is an Apache commons method called StringUtils.strip(String, String) that can do this; call it with " " as the 2nd argument.

Your attempted code has a number of bugs, and is fundamentally inefficient. If you really want to implement this yourself, then you should:

1. count the leading space characters
2. count the trailing space characters
3. if either count is non-zero, call String.substring(from, end) to create a new string containing the characters you want to keep.

This approach avoids copying any characters².

---

^{1 - The different meanings are explained in the respective javadocs. Alternatively, read the answers to Difference between String trim() and strip() methods in Java 11.}

^{2 - Actually, that depends on the implementation of String. For some implementations there will be no copying, for others a single copy is made. But either is an improvement on your approach, which entails a minimum of 2 copies, and more if there are any characters to trim.}

Answer 5

String.trim() is very old, at least to java 1.3. You don't have this?

Answer 6

The destination array newChars is not large enough to hold the values copied. You need to initialize it to the length of the data you intend to copy (so, length - 1).