How to use java String format in Scala

Question

I am trying to use a  format method of a string  But if I place  1   2  etc  in the string  java util UnknownFormatConversionException is thrown pointing to a confusing Java source code piece   private void checkText String s         int idx          If there are any     in the given string  we got a bad format        specifier      if   idx   s indexOf          -1            char c    idx  gt  s length   - 2         s charAt idx   1            throw new UnknownFormatConversionException String valueOf c              From this I understand that   char is forbidden  If so  then what should I use for argument placeholders   I use Scala 2 8

User · Answer

Instead of looking at the source code  you should read the javadoc String format   and Formatter syntax   You specify the format of the value after the    For instance for decimal integer it is d  and for String it is s   String aString    world   int aInt   20  String format  Hello   s on line  d    aString  aInt      Output    Hello  world on line 20   To do what you tried  use an argument index   you use   n     String format  Line  2 d  Value  1 s  Result  Hello  1 s at line  2 d   aString  aInt      Output   Line 20  Value world  Result  Hello world at line 20

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Although  Londo mentioned Scala s  s  string interpolator  I think Scala s  f  string interpolator is more relevant to the original question  The example used a few time in other responses could also be written  since Scala 2 10  this way   scala gt  val name    Ivan  name  String   Ivan scala gt  val thing    Scala  thing  String   Scala scala gt  val formatted   f Hello  name s  isn t  thing s cool   formatted  String   Hello Ivan  isn t Scala cool    The connection to the original question is to be aware that    formatted is defined with a string that is prefixed with the letter  f   This is the  f   formatting  string interpolator  The  f  string interpolator uses java util Formatter java lang String format uses the same java util Formatter   The nice thing about string interpolation is that it lets you see which variable is being substituted directly into the string instead of having to match it with the arguments to the String format method

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In scala   for string Interpolation we have   that saves the day and make our life much easy   For Example  You want to define a function that takes input name and age and says Hello With the name and says its age  That can be written like this   def funcStringInterpolationDemo name String age Int  s Hey   my name is  name and my age is  age    Hence   When you call this function  like this    funcStringInterpolationDemo  Shivansh  22    Its output would be    Hey   my name is Shivansh and my age is 22   You can write the code to change it in the same line  like if you want to add 10 years to the age     then function could be    def funcStringInterpolationDemo name String age Int  s Hey   my name is  name and my age is   age 10     And now the output would be    Hey   my name is Shivansh and my age is 32

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This is a list of what String format can do  The same goes for printf  int i   123  o printf     d  d  n          i  -i             123 -123  o printf     5d  5d  n        i  -i               123     123  o printf     -5d  -5d  n      i  -i             123   -123   o printf      -5d   -5d  n    i  -i              123  -123   o printf     05d  05d  n n    i  -i             00123 -0123   o printf     X  x  n   0xabc  0xabc             ABC abc  o printf     04x   x  n n   0xabc  0xabc        0abc 0xabc   double d   12345 678  o printf     f  f  n            d  -d           12345 678000       -12345 678000  o printf      f   f  n          d  -d            12345 678000   -12345 678000  o printf      f   f  n          d  -d            12345 678000   -12345 678000  o printf      2f   2f  n        d  -d           12345 68   -12345 68  o printf       2f    2f  n      d  -d           12 345 68   -12 345 68  o printf      2f    2f  n       d  -d           12345 68    12345 68   o printf     10 2f  10 2f  n    d  -d             12345 68       12345 68  o printf     010 2f  010 2f  n  d  -d           0012345 68   -012345 68   String s    Monsterbacke   o printf    n  s  n   s                         Monsterbacke  o printf     S  n   s                           MONSTERBACKE  o printf     20s  n   s                                 Monsterbacke  o printf     -20s  n   s                        Monsterbacke          o printf     7s  n   s                          Monsterbacke  o printf      7s  n   s                         Monster  o printf     20 7s  n   s                                    Monster   Date t   new Date    o printf    tT n   t                           11 01 39 o printf    tD n   t                           04 18 08 o printf    1 te   1 tb n   t                  18  Apr

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Here is a list of formatters used with String format    http   docs oracle com javase 1 5 0 docs api java util Formatter html

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You don t need to use numbers to indicate positioning   By default  the position of the argument is simply the order in which it appears in the string   Here s an example of the proper way to use this   String result   String format  The format method is  s     great       result now equals   The format method is great      You will always use a   followed by some other characters to let the method know how it should display the string     s is probably the most common  and it just means that the argument should be treated as a string   I won t list every option  but I ll give a few examples just to give you an idea      we can specify the   of decimals we want to show for a floating point  String result   String format  10   3     2f   10 0   3 0      result now equals   10   3   3 33      we can add commas to long numbers  result   String format  Today we processed   d transactions    1000000      result now equals   Today we processed 1 000 000 transactions     String format just uses a java util Formatter  so for a full description of the options you can see the Formatter javadocs   And  as BalusC mentions  you will see in the documentation that is possible to change the default argument ordering if you need to    However  probably the only time you d need   want to do this is if you are using the same argument more than once

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The official reference is the class Formatter

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Also note that Scala extends String with a number of methods  via implicit conversion to a WrappedString brought in by Predef  so you could also do the following   val formattedString    Hello  s  isn t  s cool   format  Ivan    Scala

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In Scala 2 10  val name    Ivan  val weather    sunny   s Hello  name  it s  weather today

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You can use this   String format   1 s  2 s  2 s  3 s    a    b    c      Output       a b b c

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While all the previous responses are correct  they re all in Java  Here s a Scala example   val placeholder    Hello  s  isn t  s cool   val formatted   placeholder format  Ivan    Scala     I also have a blog post about making format like Python s   operator that might be useful

[java] How to use java.String.format in Scala?

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