Duplicate string in java

Question

I want to duplicate a String by a given number separated by ,. For example:

int i=3;
String word = "a"; 
String result = String.duplicate(word, ',', i);

// result is: "a,a,a"

I know there is something like that in Ruby but I'm looking in Java. I wrote some code with a loop and then I removed the last char (which is the ,). I wondered if there is a build-in function.

I did write my own function, I just wanted to know if there is build-in for that..

Almost a duplicate of http://stackoverflow.com/questions/1235179/simple-way-to-repeat-a-string-in-java (but not quite) — Dawood ibn Kareem, Oct 07 '13 at 19:53
You may also be interested in https://bitbucket.org/adamldavis/dollar/wiki/Home — Dawood ibn Kareem, Oct 07 '13 at 19:56

score 6 · Accepted Answer · answered Oct 07 '13 at 19:49

6

Commons Lang - StringUtils#repeat:

StringUtils.repeat("a", ",", 3);

answered Oct 07 '13 at 19:49

Pavel Horal

17,782
3
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True, but I wrote it before the question was rephrased and the *"lets all write how to concatenate strings" mania* started :). – Pavel Horal Oct 07 '13 at 20:15

score 1 · Answer 2 · answered Oct 07 '13 at 19:52

1

why not write a method of your own

public String duplicate(String word, String separator, int count) {

  StringBuilder str = new StringBuilder();
  for (int i =0; i < count; i++) {
    str.append(word);
    if (i != count - 1) {
      // append comma only for more than one words
      str.append(separator);
    }
  }

   return str.toString();
}

answered Oct 07 '13 at 19:52

S4beR

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Use a `StringBuilder`. – Georgian Oct 07 '13 at 19:53

Boris the Spider · Answer 3 · 2013-10-07T19:54:17.740

Nothing in native Java to do this (besides actually doing it obviously):

public static void main(String[] args) {
    System.out.println(join("a", ",", 3));
}

public static String join(final String in, final String on, final int num) {
    if (num < 1) {
        throw new IllegalArgumentException();
    }
    final StringBuilder stringBuilder = new StringBuilder(in);
    for (int i = 1; i < num; ++i) {
        stringBuilder.append(on).append(in);
    }
    return stringBuilder.toString();
}

In Guava you could do:

Joiner.on(',').join(Collections.nCopies(3, "a"))

score 0 · Answer 4 · answered Oct 07 '13 at 20:15

0

Here's a log (n) solution:

public static String join(String string, int n){
   StringBuilder sb = new StringBuilder(string);
   StringBuilder out = new StringBuilder();
   sb.append(",");

   for (;n>0;n=n>>1){
        if (n%2==1){
           out.append(sb.toString());
        }
       sb.append(sb);
   }

   out.deleteCharAt(out.length()-1);
   return out.toString();
}

answered Oct 07 '13 at 20:15

Jason

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1

This actually does more work than a simple loop. There's not much you can do to make it faster. Only thing that I can come up with is counting amount of space required and preallocating the buffer before filling it – Sami Korhonen Oct 07 '13 at 20:22

Duplicate string in java

4 Answers4