What is a simple way to repeat a string in java

Question

I'm looking for a simple commons method or operator that allows me to repeat some String n times. I know I could write this using a for loop, but I wish to avoid for loops whenever necessary and a simple direct method should exist somewhere.

String str = "abc";
String repeated = str.repeat(3);

repeated.equals("abcabcabc");

 Create NSString by repeating another string a given number of times

I try to avoid for loops when they are not completely necessary because:

1. They add to the number of lines of code even if they are tucked away in another function.

2. Someone reading my code has to figure out what I am doing in that for a loop. Even if it is commented and has meaningful variables names, they still have to make sure it is not doing anything "clever".

3. Programmers love to put clever things in for loops, even if I write it to "only do what it is intended to do", that does not preclude someone coming along and adding some additional clever "fix".

4. They are very often easy to get wrong. For loops involving indexes tend to generate off by one bugs.

5. For loops often reuse the same variables, increasing the chance of really hard to find scoping bugs.

6. For loops increase the number of places a bug hunter has to look.

Answer 1

From Java 11 on, there's a method String::repeat that does exactly what you asked for:

String str = "abc";
String repeated = str.repeat(3);
repeated.equals("abcabcabc");

Its Javadoc says:

/**
 * Returns a string whose value is the concatenation of this
 * string repeated {@code count} times.
 * <p>
 * If this string is empty or count is zero then the empty
 * string is returned.
 *
 * @param count number of times to repeat
 *
 * @return A string composed of this string repeated
 * {@code count} times or the empty string if this
 * string is empty or count is zero
 *
 * @throws IllegalArgumentException if the {@code count} is
 * negative.
 *
 * @since 11
 */ 

Here is the shortest version (Java 1.5+ required):

repeated = new String(new char[n]).replace("\0", s);

Where n is the number of times you want to repeat the string and s is the string to repeat.

No imports or libraries needed.

Hope it helps and for more to learn about Java, enroll with Java certification course now.

Comments

Thanks Frankie for this code, I used it in my java project at school.

Answer 2

Here is the shortest version (Java 1.5+ required):

repeated = new String(new char[n]).replace("\0", s);

Where n is the number of times you want to repeat the string and s is the string to repeat.

No imports or libraries needed.

Answer 3

String repeat() – Repeat string N times in Java

Learn to repeat a given string N times, to produce a new string that contains all the repetitions, though a simple Java program. We will use method Sting.repeat(N) (since Java 11) and using regular expression

1. String.repeat() API [Since Java 11]

This method returns a string whose value is the concatenation of given string repeated count times. If the string is empty or count is zero then the empty string is returned.

1.1. Syntax

/** * Parameters: * count - number of times to repeat * * Returns: * A string composed of this string repeated count times or the empty string if this string is empty or count is zero * * Throws: * IllegalArgumentException - if the count is negative. */ public String repeat​(int count)

Answer 4

There is already answer wriiten using StringBuilder without any external libraries.

But if your project contains Apache Common lang jar, you can use

• public static String repeat(String str, 

• int repeat) 

Repeat a String repeat times to form a new String.

• StringUtils.repeat(null, 2) = null 

• StringUtils.repeat("", 0) = "" 

• StringUtils.repeat("", 2) = "" 

• StringUtils.repeat("a", 3) = "aaa" 

• StringUtils.repeat("ab", 2) = "abab" 

• StringUtils.repeat("a", -2) = "" 

StringUtils (Apache Commons Lang 3.7 API)

It has lot of utility classes which always reduces boiler plate code from your project.