Create a string with n characters

Question

Is there a way in java to create a string with a specified number of a specified character? In my case, I would need to create a string with 10 spaces. My current code is:

Answer 1

In most cases you only need Strings upto a certains length, say 100 spaces. You could prepare an array of Strings where the index number is equal to the size of the space-filled string and lookup the string, if the required length is within the limits or create it on demand if it's outside the boundary.

Answer 2

how about this?

public String fillSpaces(int len) {
    /* the spaces string should contain spaces exceeding the max needed */  
    String spaces = "                                                   ";
    return spaces.substring(0,len);
}

EDIT: I've written a simple code to test the concept and here what i found.

Method 1: adding single space in a loop:

  public String execLoopSingleSpace(int len){
    StringBuilder sb = new StringBuilder();

    for(int i=0; i < len; i++) {
        sb.append(' ');
    }

    return sb.toString();
  }

Method 2: append 100 spaces and loop, then substring:

  public String execLoopHundredSpaces(int len){
    StringBuilder sb = new StringBuilder("          ")
            .append("          ").append("          ").append("          ")
            .append("          ").append("          ").append("          ")
            .append("          ").append("          ").append("          ");

    for (int i=0; i < len/100 ; i++) {
        sb.append("          ")
            .append("          ").append("          ").append("          ")
            .append("          ").append("          ").append("          ")
            .append("          ").append("          ").append("          ");
    }

    return sb.toString().substring(0,len);
  }

The result I get creating 12,345,678 spaces:

C:\docs\Projects> java FillSpace 12345678
method 1: append single spaces for 12345678 times. Time taken is **234ms**. Length of String is 12345678
method 2: append 100 spaces for 123456 times. Time taken is **141ms**. Length of String is 12345678
Process java exited with code 0

and for 10,000,000 spaces:

C:\docs\Projects> java FillSpace 10000000
method 1: append single spaces for 10000000 times. Time taken is **157ms**. Length of String is 10000000
method 2: append 100 spaces for 100000 times. Time taken is **109ms**. Length of String is 10000000
Process java exited with code 0

combining direct allocation and iteration always takes less time, on average 60ms less when creating huge spaces. For smaller sizes, both results are negligible.

But please continue to comment :-)

Answer 3

Use StringUtils: StringUtils.repeat(' ', 10)

Answer 4

Just replace your StringBuffer with a StringBuilder. Hard to beat that.

If your length is a big number, you might implement some more efficient (but more clumsy) self-appendding, duplicating the length in each iteration:

 public static String dummyString(char c, int len) {
  if( len < 1 ) return "";
  StringBuilder sb = new StringBuilder(len).append(c);
  int remnant = len - sb.length();
  while(remnant  > 0) {
   if( remnant  >= sb.length() ) sb.append(sb);
   else sb.append(sb.subSequence(0, remnant));
   remnant  = len - sb.length();
  }
  return sb.toString();
 }

Also, you might try the Arrays.fill() aproach (FrustratedWithFormsDesigner's answer).

Answer 5

In Java 8 you can use String.join:

String.join("", Collections.nCopies(n, s));

Answer 6

I think this is the less code it's possible, it uses Guava Joiner class:

Joiner.on("").join(Collections.nCopies(10, " "));