Java - Create a new String instance with specified length and filled with specific character Best solution

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I did check the other questions  this question has its focus on solving this particular question the most efficient way    Sometimes you want to create a new string with a specified length  and with a default character filling the entire string   ie  it would be cool if you could do new String 10       and create a new String from there  with a length of 10 characters all having a     Because such a constructor does not exist  and you cannot extend from String  you have either to create a wrapper class or a method to do this for you   At this moment I am using this   protected String getStringWithLengthAndFilledWithCharacter int length  char charToFill        char   array   new char length       int pos   0      while  pos  lt  length            array pos    charToFill          pos              return new String array       It still lacks any checking  ie  when length is 0 it will not work   I am constructing the array first because I believe it is faster than using string concatination or using a StringBuffer to do so   Anyone else has a better sollution

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To improve performance you could have a single predefined sting if you know the max length like:

String template = "####################################";

And then simply perform a substring once you know the length.

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One extra note  it seems that all public ways of creating a new String instance involves necessarily the copy of whatever buffer you are working with  be it a char    a StringBuffer or a StringBuilder  From the String javadoc  and is repeated in the respective toString methods from the other classes       The contents of the character array are copied  subsequent modification of   the character array does not affect   the newly created string    So you ll end up having a possibly big memory copy operation after the  fast filling  of the array  The only solution that may avoid this issue is the one from  mlk  if you can manage working directly with the proposed CharSequence implementation  what may be the case    PS  I would post this as a comment but I don t have enough reputation to do that yet

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char   chars   new char 10   Arrays fill chars        String text   new String chars

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You can use a while loop like this   String text    Hello   while  text length    lt  10    text           System out println text     Will give you   Hello        Or get the same result with a custom method       public static String extendString String text  String symbol  Integer len            while  text length    lt  len    text    symbol            return text          Then just call   extendString  Hello        10    It may also be a good idea to set a length check to prevent infinite loop

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Mi solution       pw    1321       if  pw length    lt  16         for int x   pw length     x  lt  16   x             pw                          The output     1321

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No need to do the loop  and using just standard Java library classes   protected String getStringWithLengthAndFilledWithCharacter int length  char charToFill      if  length  gt  0        char   array   new char length       Arrays fill array  charToFill       return new String array         return         As you can see  I also added suitable code for the length    0 case

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Apache Commons Lang  probably useful enough to be on the classpath of any non-trivial project  has StringUtils repeat     String filled   StringUtils repeat      10     Easy

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Simply use the StringUtils class from apache commons lang project  You have a leftPad method   StringUtils leftPad  foobar   10           Returns      foobar

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In Java 11  you have repeat   String s        s   s repeat 1      Although at the time of writing still subject to change

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The above is fine  Do you mind if I ask you a question - Is this causing you a problem  It seams to me you are optimizing before you know if you need to   Now for my over engineered solution  In many  thou not all  cases you can use CharSequence instead of a String   public class OneCharSequence implements CharSequence     private final char value    private final int length    public OneCharSequence final char value  final int length        this value   value      this length   length        public char   charAt int index          if index  lt  length  return value       throw new IndexOutOfBoundsException          public int length         return length        public CharSequence subSequence int start  int end         return new OneCharSequence value   end-start          public String toString         char   array   new char length       Arrays fill array  value       return new String array

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Solution using Google Guava  since I prefer it to Apache Commons-Lang          Returns a String with exactly the given length composed entirely of    the given character      param length the length of the returned string     param c the character to fill the String with     public static String stringOfLength final int length  final char c        return Strings padEnd     length  c

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Solution using Google Guava  String filled   Strings repeat      10

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public static String fillString int count char c        StringBuilder sb   new StringBuilder  count        for  int i 0  i lt count  i               sb append  c               return sb toString        What is wrong

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using Dollar is simple   String filled          repeat 10  toString       produces

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Some possible solutions   This creates a String with length-times  0  filled and replaces then the  0  with the charToFill  old school    String s   String format   0    length    d   0  replace  0   charToFill     This creates a List containing length-times Strings with charToFill and then joining the List into a String   String s   String join     Collections nCopies length  String valueOf charToFill       This creates a unlimited java8 Stream with Strings with charToFill  limits the output to length and collects the results with a String joiner  new school    String s   Stream generate    - gt  String valueOf charToFill   limit length  collect Collectors joining

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Try this Using the substring int start  int end   method  String myLongString    abcdefghij   if  myLongString  length    gt   10  String shortStr   myLongString substring 0  5            this will return abcde

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Try this jobber  String stringy  null   byte   buffer    new byte 100000               for  int i   0  i  lt  buffer length  i                  buffer i   0                         stringy  StringUtils toAsciiString buffer

[java] Java - Create a new String instance with specified length and filled with specific character. Best solution?

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