Java String - add character n-times

Question

Is there a simple way to add a character or another String n-times to an existing String  I couldn   t find anything in String  Stringbuilder  etc

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In addition to the answers above  you should initialize the StringBuilder with an appropriate capacity  especially that you already know it  For example   int capacity   existingString length     n   appendableString length    StringBuilder builder   new StringBuilder capacity

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Keep in mind that if the  n  is large  it might not be such a great idea to use     since every time you add another String through     the JVM will create a brand new object  plenty of info on this around     Something like   StringBuilder b   new StringBuilder existing string   for int i   0  i lt n  i         b append  other string      return b toString      Not actually coding this in an IDE  so minor flaws may occur  but this is the basic idea

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For the case of repeating a single character  not a String   you could use Arrays fill     String original    original      char c    c     int number   9     char   repeat   new char number     Arrays fill repeat  c     original    new String repeat

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In case of Java 8 you can do   int n   4  String existing          String result   existing   String join     Collections nCopies n           Output             In Java 8 the String join method was added  But Collections nCopies is even in Java 5

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public String appendNewStringToExisting String exisitingString  String newString  int number        StringBuilder builder   new StringBuilder exisitingString       for int iDx   0  iDx  lt  number  iDx             builder append newString             return builder toString

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You are able to do this using Java 8 stream APIs  The following code creates the string  cccc  from  c    String s    c   int n   4  String sRepeated   IntStream range 0  n  mapToObj i - gt  s  collect Collectors joining

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Here is a simple way    for int i 0 i lt n i        yourString   yourString    what you want to append continiously

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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  lt  howmany  i            out append what       return out toString        using   public static void main String    args        String res      long time       for  int j   0  j  lt  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

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String toAdd    toAdd    StringBuilder s   new StringBuilder     for int count   0  count  lt  MAX  count           s append toAdd         String output   s toString

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for int i   0  i  lt  n  i          existing string     c       but you should use StringBuilder instead  and save memory  int n   3  String existing string    string   StringBuilder builder   new StringBuilder existing string   for  int i   0  i  lt  n  i          builder append   append        System out println builder toString

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Apache commons-lang3 has StringUtils repeat String  int   with this one you can do  for simplicity  not with StringBuilder    String original  original   original   StringUtils repeat  x   n     Since it is open source  you can read how it is written  There is a minor optimalization for small n-s if I remember correctly  but most of the time it uses StringBuilder

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How I did it   final int numberOfSpaces   22  final char   spaceArray   new char numberOfSpaces   Arrays fill spaces          Now add it to your StringBuilder  stringBuilder append spaceArray     or String  final String spaces   String valueOf spaceArray

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You can use Guava s Strings repeat method   String existingString       existingString    Strings repeat  foo   n

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Use this   String input    original   String newStr    new     new string to be added int n   10    no of times we want to add input   input   new String new char n   replace   0   newStr

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Its better to use StringBuilder instead of String because String is an immutable class and it cannot be modified once created  in String each concatenation results in creating a new instance of the String class with the modified string

[java] Java: String - add character n-times

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