What is the easiest way to generate a String of n repeated characters?

Question

Given a character c and a number n, how can I create a String that consists of n repetitions of c? Doing it manually is too cumbersome:

StringBuilder sb = ne         


        

Answer 1

Here is an O(logN) method, based on the standard binary powering algorithm:

public static String repChar(char c, int reps) {
    String adder = Character.toString(c);
    String result = "";
    while (reps > 0) {
        if (reps % 2 == 1) {
            result += adder;
        }
        adder += adder;
        reps /= 2;
    }        
    return result;
}

Negative values for reps return the empty string.

Answer 2

Google Guava Time!

Strings.repeat("a", 3)

http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/base/Strings.html

Answer 3

To have an idea of the speed penalty, I have tested two versions, one with Array.fill and one with StringBuilder.

public static String repeat(char what, int howmany) {
    char[] chars = new char[howmany];
    Arrays.fill(chars, what);
    return new String(chars);
}

and

public static String repeatSB(char what, int howmany) {
    StringBuilder out = new StringBuilder(howmany);
    for (int i = 0; i < howmany; i++)
        out.append(what);
    return out.toString();
}

using

public static void main(String... args) {
    String res;
    long time;

    for (int j = 0; j < 1000; j++) {
        res = repeat(' ', 100000);
        res = repeatSB(' ', 100000);
    }
    time = System.nanoTime();
    res = repeat(' ', 100000);
    time = System.nanoTime() - time;
    System.out.println("elapsed repeat: " + time);

    time = System.nanoTime();
    res = repeatSB(' ', 100000);
    time = System.nanoTime() - time;
    System.out.println("elapsed repeatSB: " + time);
}

(note the loop in main function is to kick in JIT)

The results are as follows:

elapsed repeat  : 65899
elapsed repeatSB: 305171

It is a huge difference

Answer 4

string result = new StringBuilder().Append('c', n).ToString();

Answer 5

take look at this sample

Integer  n=10;
String s="a";
String repeated = new String(new char[n]).replace("\0", s);

answer taken form Simple way to repeat a String in java so vote up there

Answer 6

If you can, use StringUtils from Apache Commons Lang:

StringUtils.repeat("ab", 3);  //"ababab"