Simple way to repeat a string

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 f

Answer 1

using only JRE classes (System.arraycopy) and trying to minimize the number of temp objects you can write something like:

public static String repeat(String toRepeat, int times) {
    if (toRepeat == null) {
        toRepeat = "";
    }

    if (times < 0) {
        times = 0;
    }

    final int length = toRepeat.length();
    final int total = length * times;
    final char[] src = toRepeat.toCharArray();
    char[] dst = new char[total];

    for (int i = 0; i < total; i += length) {
        System.arraycopy(src, 0, dst, i, length);
    }

    return String.copyValueOf(dst);
}

EDIT

and without loops you can try with:

public static String repeat2(String toRepeat, int times) {
    if (toRepeat == null) {
        toRepeat = "";
    }

    if (times < 0) {
        times = 0;
    }

    String[] copies = new String[times];
    Arrays.fill(copies, toRepeat);
    return Arrays.toString(copies).
              replace("[", "").
              replace("]", "").
              replaceAll(", ", "");
}

EDIT 2

using Collections is even shorter:

public static String repeat3(String toRepeat, int times) {
    return Collections.nCopies(times, toRepeat).
           toString().
           replace("[", "").
           replace("]", "").
           replaceAll(", ", "");
}

however I still like the first version.

Answer 2

Not the shortest, but (i think) the fastest way is to use the StringBuilder:

 /**
   * Repeat a String as many times you need.
   *
   * @param i - Number of Repeating the String.
   * @param s - The String wich you want repeated.
   * @return The string n - times.
   */
  public static String repeate(int i, String s) {
    StringBuilder sb = new StringBuilder();
    for (int j = 0; j < i; j++)
      sb.append(s);
    return sb.toString();
  }

Answer 3

If you are worried about performance, just use a StringBuilder inside the loop and do a .toString() on exit of the Loop. Heck, write your own Util Class and reuse it. 5 Lines of code max.

Answer 4

String::repeat

". ".repeat( 7 )  // Seven period-with-space pairs: . . . . . . . 

New in Java 11 is the 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
 */ 

Answer 5

If you are using Java <= 7, this is as "concise" as it gets:

// create a string made up of n copies of string s
String.format("%0" + n + "d", 0).replace("0", s);

In Java 8 and above there is a more readable way:

// create a string made up of n copies of string s
String.join("", Collections.nCopies(n, s));

Finally, for Java 11 and above, there is a new repeat​(int count) method specifically for this(link)

"abc".repeat(12);

Alternatively, if your project uses java libraries there are more options.

For Apache Commons:

StringUtils.repeat("abc", 12);

For Google Guava:

Strings.repeat("abc", 12);

Answer 6

I created a recursive method that do the same thing you want.. feel free to use this...

public String repeat(String str, int count) {
    return count > 0 ?  repeat(str, count -1) + str: "";
}

i have the same answer on Can I multiply strings in java to repeat sequences?