What is the purpose of String.strip() method of Java 11?

The purpose of the String.strip() method in Java 11 is to remove whitespaces from both the beginning and end of a string. This is very similar to the String.trim() method available in earlier versions of Java, but there is a key difference between them.

Here’s the difference:

  • String.strip(): Introduced in Java 11, strip() uses the unicode definition of whitespace. It removes not only space characters but also all other types of unicode-defined spaces, such as the thin space \u2009, etc.
  • String.trim(): Available from Java 1.0, trim() is more limited. It considers a whitespace to be any character whose ASCII value is less than or equal to 32 (a space, tab, newline, and a few other control characters).

Here are examples of how they work:

package org.kodejava.lang;

public class StringStripExample {
    public static void main(String[] args) {
        // String.strip()
        String first = " \u2009Hello  ";
        System.out.println(first.strip()); // Outputs "Hello"

        // String.trim()
        String second = " \u2009Hello  ";
        System.out.println(second.trim()); // Outputs "\u2009Hello"



Thus, strip() method is more comprehensive in removing different types of whitespace defined in Unicode, while trim() only removes ASCII control characters and spaces.

There are also String.stripLeading() and String.stripTrailing() methods that were introduced in Java 11, and they are similar to the strip() method, but they only remove the whitespace characters from either the beginning or the end of the string, respectively.

Here is what they do:

  • String.stripLeading(): This method removes any leading whitespace from the string. “Leading” in this context means any whitespace characters at the beginning of the string.
  • String.stripTrailing(): This method removes any trailing whitespace from the string. “Trailing” in this context means any whitespace characters at the end of the string.

Both stripLeading() and stripTrailing() use the Unicode definition of whitespace, the same as strip() method.

Here are examples of how they work:

package org.kodejava.lang;

public class StringStripLeadingTrailingExample {
    public static void main(String[] args) {
        // Strip leading whitespace
        String first = " \u2009Hello World  ";
        System.out.println(first.stripLeading());  // Outputs "Hello World  "

        // Strip trailing whitespace
        String second = " \u2009Hello World  ";
        System.out.println(second.stripTrailing()); // Outputs " \u2009Hello World"


Hello World  
  Hello World

As demonstrated, stripLeading() removed the whitespace characters from the front of the string, and stripTrailing() removed the whitespace characters from the end of the string.

While \u00A0 is technically a type of whitespace (specifically, a non-breaking space or NBSP), it isn’t considered as such by the strip(), stripLeading(), and stripTrailing() methods, which follow the Character.isWhitespace(char) method’s definition of what constitutes a whitespace character.

According to the Java documentation, the Character.isWhitespace(char) method, which the strip() methods use, considers the following characters as whitespace:

  • ‘\n’ U+000A LINE FEED
  • ‘\f’ U+000C FORM FEED
  • ‘\u001C’ U+001C FILE SEPARATOR
  • ‘\u001D’ U+001D GROUP SEPARATOR
  • ‘\u001E’ U+001E RECORD SEPARATOR
  • ‘\u001F’ U+001F UNIT SEPARATOR
  • SPACE_SEPARATOR category types

The \u2009 (thin space) and \u0020 (space) are part of SPACE_SEPARATOR category according to Unicode standard and will be correctly stripped.

The \u00A0 (non-breaking space) is actually part of a different category called the NO-BREAK_SPACE and is not considered whitespace by Character.isWhitespace(char), so it won’t be stripped.

How do I use String.join() method in Java?

The String.join() method in Java is a static method added in Java 8 to the java.lang.String class. The String.join() is a static utility method used to concatenate multiple strings, arrays or collections (like lists and sets) of strings. This method makes it easier to join multiple strings with a specific delimiter. A delimiter is a sequence of characters used to separate strings.

This method returns a new String composed of copies of the CharSequence elements joined together with a copy of the specified delimiter. This method saves us from writing boilerplate loop code just for concatenating strings with a delimiter.

Here is an example of how you can use it:

package org.kodejava.lang;

import java.util.Arrays;
import java.util.List;

public class StringJoinList {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("Java", "is", "cool");
        String result = String.join(" ", list);


Java is cool

In this example, String.join() takes two parameters:

  1. A delimiter that is a CharSequence (like a String) that is placed between each joined String.
  2. An Iterable object like a List or a Set, over which the method iterates and joins all elements into a single String.

You can also use String.join() with an array of elements:

package org.kodejava.lang;

public class StringJoinArray {
    public static void main(String[] args) {
        String[] array = new String[]{"Java", "is", "cool"};
        String result = String.join(" ", array);


Java is cool

In this case, String.join() still takes a delimiter as the first argument, but the second argument is an Array of elements to be joined.

How do I create a string of repeated characters?

The following code demonstrates how to create a string of repeated characters. We use the String.repeat(int count) method introduced in Java 11. This method takes one parameter of type int which is the number of times to repeat the string. The count must be a positive number, a negative number will cause this method to throw java.lang.IllegalArgumentException.

In the snippet below, we use the method to repeat characters and draw some triangles. We combine the repeat() method with a for loop to draw the triangles.

package org.kodejava.basic;

public class StringRepeatDemo {
    public static void main(String[] args) {
        String star = "*";
        String fiveStars = star.repeat(5);
        System.out.println("fiveStars = " + fiveStars);

        String arrow = "-->";
        String arrows = arrow.repeat(10);
        System.out.println("arrows    = " + arrows);

The outputs of the code snippet above are:

fiveStars = *****
arrows    = -->-->-->-->-->-->-->-->-->-->
package org.kodejava.basic;

public class StringRepeatDemo {
    public static void main(String[] args) {
        String asterisk = "#";
        for (int i = 1; i <= 10; i++) {

The outputs of the code snippet above are:

package org.kodejava.basic;

public class StringRepeatDemo {
    public static void main(String[] args) {
        int height = 10;
        for (int i = 1, j = 1; i <= height; i++, j += 2) {
            System.out.println(" ".repeat(height - i) + "*".repeat(j));

The outputs of the code snippet above are:


How do I generate random alphanumeric strings?

The following code snippet demonstrates how to use RandomStringGenerator class from the Apache Commons Text library to generate random strings. To create an instance of the generator we can use the RandomStringGenerator.Builder() class build() method. The builder class also helps us to configure the properties of the generator. Before calling the build() method we can set the properties of the builder using the following methods:

  • withinRange() to specifies the minimum and maximum code points allowed in the generated string.
  • filteredBy() to limits the characters in the generated string to those that match at least one of the predicates supplied. Some enum for the predicates: CharacterPredicates.DIGITS, CharacterPredicates.LETTERS.
  • selectFrom() to limits the characters in the generated string to those who match at supplied list of Character.
  • usingRandom() to overrides the default source of randomness.

After configuring and building the generator based the properties defined, we can generate the random strings using the generate() methods of the RandomStringGenerator. There are two methods available:

  • generate(int length) generates a random string, containing the specified number of code points.
  • generate(int minLengthInclusive, int maxLengthInclusive) generates a random string, containing between the minimum (inclusive) and the maximum (inclusive) number of code points.

And here is your code snippet:

package org.kodejava.commons.text;

import org.apache.commons.text.CharacterPredicates;
import org.apache.commons.text.RandomStringGenerator;

public class RandomStringDemo {
    public static void main(String[] args) {
        RandomStringGenerator generator = new RandomStringGenerator.Builder()
                .withinRange('0', 'z')
                .filteredBy(CharacterPredicates.DIGITS, CharacterPredicates.LETTERS)

        for (int i = 0; i < 10; i++) {
            System.out.println(generator.generate(10, 20));

Below are examples of generated random alphanumeric strings:


Apache Logo

Maven Dependencies


Maven Central

How do I align string print out in left, right, center alignment?

The following code snippet will teach you how to align string in left, right or center alignment when you want to print out string to a console. We will print the string using the printf(String format, Object... args) method. The format specifier / parameter defines how the string will be formatted for output and the args is the value that will be formatted.

The format parameter / specifier include flags, width, precision and conversion-characters in the order shown below. The square brackets in the notation means the part is an optional parameter.

% [flags] [width] [.precision] conversion-character
Flags Description
- left-align the output, when not specified the default is to right-align
+ print (+) or (-) sign for numeric value
0 zero padded a numeric value
, comma grouping separator for number greater that 1000
space will output a (-) symbol for negative value and a space if positive
Conversion Description
s string, use capital S to uppercase the strings
c character, use capital C to uppercase the characters
d integer: byte, short, integer, long
f floating point number: float, double
n new line

Width: Defines the field width for printing out the value of argument. It also represents the minimum number of characters to
be printed out to the output.

Precision: For floating-point conversion the precision define the number of digits of precision in a floating point value. For string value this will extract the substring.

To center the string for output we use the StringUtils.center() method from the Apache Commons Lang library. This method will center-align the string str in a larger string of size using the default space character (‘ ‘). You can supply the third parameter to define your own space character / string.

package org.kodejava.lang;

import org.apache.commons.lang3.StringUtils;

import java.time.LocalDate;
import java.time.Month;
import java.time.temporal.ChronoUnit;

public class StringAlignment {
    private static final Object[][] people = {
            {"Alice", LocalDate.of(2000, Month.JANUARY, 1)},
            {"Bob", LocalDate.of(1989, Month.DECEMBER, 15)},
            {"Carol", LocalDate.of(1992, Month.JULY, 24)},
            {"Ted", LocalDate.of(2006, Month.MARCH, 13)},

    public static void main(String[] args) {
        String nameFormat = "| %1$-20s | ";
        String dateFormat = " %2$tb %2$td, %2$tY  | ";
        String ageFormat = " %3$3s |%n";
        String format = nameFormat.concat(dateFormat).concat(ageFormat);
        String line = new String(new char[48]).replace('\0', '-');

                StringUtils.center("Name", 22),
                StringUtils.center("Birth Date", 16),
                StringUtils.center("Age", 6));

        for (Object[] data : people) {
                    data[0], data[1],
                    ChronoUnit.YEARS.between((LocalDate) data[1], LocalDate.now()));


Here is the output of our code snippet above:

|         Name         |   Birth Date   | Age  |
| Alice                |  Jan 01, 2000  |   17 |
| Bob                  |  Dec 15, 1989  |   27 |
| Carol                |  Jul 24, 1992  |   24 |
| Ted                  |  Mar 13, 2006  |   10 |

Maven Dependencies

<!-- https://search.maven.org/remotecontent?filepath=org/apache/commons/commons-lang3/3.12.0/commons-lang3-3.12.0.jar -->

Maven Central