How to insert a character in a string at a certain position

Question

I m getting in an int with a 6 digit value  I want to display it as a String with a decimal point     at 2 digits from the end of int  I wanted to use a float but was suggested to use String for a better display output  instead of 1234 5 will be 1234 50   Therefore  I need a function that will take an int as parameter and return the properly formatted String with a decimal point 2 digits from the end   Say   int j  123456  Integer toString j       processing       output   1234 56

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For Kotlin dudes    from the accepted answer   MikeThomsen s   fun String insert index  Int  string  String   String       return this substring 0  index    string   this substring index  this length      Test     ThisTest  insert 4   Is   should equal  ThisIsTest

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I think a simpler and more elegant solution to insert a String in a certain position would be this one-liner   target replaceAll          position           1    insert     For example  to insert a missing   into a time String    -0300  replaceAll      3       1       What it does is  matches position characters from the beginning of the string  groups that  and replaces the group with itself   1  followed by the insert string  Mind the replaceAll  even though there s always one occurrence  because the first parameter must be a regex   Of course it does not have the same performance as the StringBuilder solution  but I believe the succinctness and elegance as a simple and easier to read one-liner  compared to a huge method  is sufficient for making it the preferred solution in most non performance-critical use-cases   Note I m solving the generic problem in the title for documentation reasons  of course if you are dealing with decimal numbers you should use the domain-specific solutions already proposed

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public static void main String   args        char ch  m       String str  Hello  k String valueOf ch  b c       System out println str        int index 3      b str substring 0 index-1        c str substring index-1 str length         str b k c

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In most use-cases  using a StringBuilder  as already answered  is a good way to do this  However  if performance matters  this may be a good alternative          Insert the  insert  String at the index  position  into the  target  String                 insertAt  AC   0      - gt   AC     insertAt  AC   1   xxx   - gt   AxxxC     insertAt  AB   2   C   - gt   ABC             public static String insertAt final String target  final int position  final String insert        final int targetLen   target length        if  position  lt  0    position  gt  targetLen            throw new IllegalArgumentException  position     position             if  insert isEmpty              return target            if  position    0            return insert concat target         else if  position    targetLen            return target concat insert             final int insertLen   insert length        final char   buffer   new char targetLen   insertLen       target getChars 0  position  buffer  0       insert getChars 0  insertLen  buffer  position       target getChars position  targetLen  buffer  position   insertLen       return new String buffer

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If you are using a system where float is expensive  e g  no FPU  or not allowed  e g  in accounting  you could use something like this       for  int i   1  i  lt  100000  i    2            String s    00    i          System out println s substring Math min 2  s length   - 2   s length   - 2          s substring s length   - 2            Otherwise the DecimalFormat is the better solution   the StringBuilder variant above won t work with small numbers   lt 100

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String format   0d  02d   d   100  d   100

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Create given String and make with size 30 String str    Hello How Are You       Creating StringBuffer Object for right padding StringBuffer stringBufferRightPad   new StringBuffer str   while  stringBufferRightPad length    lt  30        stringBufferRightPad insert stringBufferRightPad length             System out println  after Left padding       stringBufferRightPad   System out println  after Left padding       stringBufferRightPad toString         Creating StringBuffer Object for right padding StringBuffer stringBufferLeftPad   new StringBuffer str   while  stringBufferLeftPad length    lt  30        stringBufferLeftPad insert 0          System out println  after Left padding       stringBufferLeftPad   System out println  after Left padding       stringBufferLeftPad toString

User · Answer

Using ApacheCommons3 StringUtils  you could also do  int j   123456  String s   Integer toString j   int pos   s length  -2   s   StringUtils overlay s      pos  pos     it s basically substring concatenation but shorter if you don t mind using libraries  or already depending on StringUtils

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Try this    public String ConvertMessage String content sendout              use unicode  004E00650077  need to change to hex   amp  x004E amp  x 0065 amp  x 0077   first           String resultcontent sendout               int i   4          int lengthwelcomemsg   content sendout length   i          for int nadd 0 nadd lt lengthwelcomemsg nadd                 if nadd    0                   resultcontent sendout     amp  x  content sendout substring nadd i   nadd i  i       amp  x                else if nadd    lengthwelcomemsg-1                   resultcontent sendout    content sendout substring nadd i   nadd i  i                      else                  resultcontent sendout    content sendout substring nadd i   nadd i  i       amp  x                                   return resultcontent sendout

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As mentioned in comments  a StringBuilder is probably a faster implementation than using a StringBuffer  As mentioned in the Java docs       This class provides an API compatible with StringBuffer  but with no guarantee of synchronization  This class is designed for use as a drop-in replacement for StringBuffer in places where the string buffer was being used by a single thread  as is generally the case   Where possible  it is recommended that this class be used in preference to StringBuffer as it will be faster under most implementations    Usage     String str   Integer toString j   str   new StringBuilder str  insert str length  -2       toString      Or if you need synchronization use the StringBuffer with similar usage    String str   Integer toString j   str   new StringBuffer str  insert str length  -2       toString

User · Answer

You could use   System out printf   4 2f n     float 12345  100      As per the comments  12345 100 0 would be better  as would the use of double instead of float

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int j   123456  String x   Integer toString j   x   x substring 0  4          x substring 4  x length

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int yourInteger   123450  String s   String format   6 2f   yourInteger   100 0   System out println s

[java] How to insert a character in a string at a certain position?

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