Java Trim String Examples (Trim Start, End)

This Java article uses the String trim method. It implements methods to trim starts and ends of strings.
Trim. Strings often contain leading or trailing whitespace. For processing the string data, these spaces are not always useful. And sometimes they cause issues.
With trim, we remove them. Trim in Java removes whitespace (including newlines, tabs and spaces) from both the left and right. Custom methods may be used for more specific purposes.
First example. This program declares and populates an array of 5 strings. These strings have leading or trailing whitespace—spaces, tabs and newlines.String Arrays

Trim: This method is called on the string to be trimmed, which must not be null. It returns a new, modified string.

Tip: We must assign the result of trim() to a variable (or pass it directly to a method) for it to be of any use.

Java program that uses trim method public class Program { public static void main(String[] args) { String[] values = { " cat", "dog ", " =bird= ", "fish\t", "line\n\n\n" }; // Trim each value in the string array. for (String value : values) { // Call the trim method. String trimmed = value.trim(); // Display the strings. System.out.print("[" + trimmed + "]"); System.out.println("[" + value + "]"); } } } Output [cat][ cat] [dog][dog ] [=bird=][ =bird= ] [fish][fish ] [line][line ]
Trim start, end. This program implements two custom methods. We use the replaceFirst method to replace whitespace at the start or end of a string. So we trim on just one side.Replace: replaceFirst

Pattern: The "\s" sequence means "whitespace character" and "\\s+" is an escaped sequence. It means one or more whitespace characters.

Java program that trims starts and ends public class Program { public static String trimEnd(String value) { // Use replaceFirst to remove trailing spaces. return value.replaceFirst("\\s+$", ""); } public static String trimStart(String value) { // Remove leading spaces. return value.replaceFirst("^\\s+", ""); } public static void main(String[] args) { String value = " /Test? "; // Use custom trimEnd and trimStart methods. System.out.println("[" + trimEnd(value) + "]"); System.out.println("[" + trimStart(value) + "]"); } } Output [ /Test?] [/Test? ] Pattern ^ The start of a string. \s+ One or more space characters. $ The end of a string.
Performance. Often, calling trim() is unnecessary. If trim is used and it is not needed, removing it will make a program faster. This could cause a behavior change.

Caution: More than anything else, I have found performance improvements to cause program bugs.

Whitespace. Sometimes we need to handle whitespace characters within strings, not just on their starts or ends. With regular expressions, or parsers, we condense or remove spaces.Whitespace
Chop, chomp and strip. In other languages, like Ruby or Perl, we invoke the chop and chomp methods. In Python we use strip() to remove whitespace on starts and ends.
These methods are similar. When a file is read, and lines may have useless (or invalid) whitespace on the ends, these methods are needed. Trim() is a simple and clear call.
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