Sprintf equivalent in Java

Question

Printf got added to Java with the 1 5 release but I can t seem to find how to send the output to a string rather than a file  which is what sprintf does in C   Does anyone know how to do this

User · Answer

You can do a printf to anything that is an OutputStream with a PrintStream. Somehow like this, printing into a string stream:

PrintStream ps = new PrintStream(baos);
ps.printf("there is a %s from %d %s", "hello", 3, "friends");
System.out.println(baos.toString());
baos.reset(); //need reset to write new string
ps.printf("there is a %s from %d %s", "flip", 5, "haters");
System.out.println(baos.toString());
baos.reset();

The string stream can be created like this ByteArrayOutputStream:

ByteArrayOutputStream baos = new ByteArrayOutputStream();

User · Answer

Store the formatted string in  result  String result   String format   4d   i   j       Write the result to standard output System out println  result      See format and its syntax

User · Answer

Strings are immutable types  You cannot modify them  only return new string instances   Because of that  formatting with an instance method makes little sense  as it would have to be called like   String formatted     s   s  format key  value     The original Java authors  and  NET authors  decided that a static method made more sense in this situation  as you are not modifying the target  but instead calling a format method and passing in an input string   Here is an example of why format   would be dumb as an instance method  In  NET  and probably in Java   Replace   is an instance method   You can do this     I Like Wine  Replace  Wine   Beer      However  nothing happens  because strings are immutable  Replace   tries to return a new string  but it is assigned to nothing   This causes lots of common rookie mistakes like   inputText Replace        20      Again  nothing happens  instead you have to do   inputText   inputText Replace       20      Now  if you understand that strings are immutable  that makes perfect sense  If you don t  then you are just confused  The proper place for Replace   would be where format   is  as a static method of String    inputText   String Replace inputText         20      Now there is no question as to what s going on   The real question is  why did the authors of these frameworks decide that one should be an instance method  and the other static  In my opinion  both are more elegantly expressed as static methods   Regardless of your opinion  the truth is that you are less prone to make a mistake using the static version  and the code is easier to understand  No Hidden Gotchas    Of course there are some methods that are perfect as instance methods  take String Length    int length    123  Length      In this situation  it s obvious we are not trying to modify  123   we are just inspecting it  and returning its length  This is a perfect candidate for an instance method   My simple rules for Instance Methods on Immutable Objects    If you need to return a new instance of the same type  use a static method  Otherwise  use an instance method

User · Answer

Since Java 13 you have formatted 1 method on String  which was added along with text blocks as a preview feature 2  You can use it instead of String format   Assertions assertEquals      quot  s  d   3f quot  formatted  quot foo quot   123  7 89       quot foo 123 7 890 quot

User · Answer

Both solutions workto simulate printf  but in a different way  For instance  to convert a value to a hex string  you have the 2 following solutions    with format    closest to sprintf     final static String HexChars    0123456789abcdef    public static String getHexQuad long v        String ret      if v  gt  0xffff  ret   getHexQuad v  gt  gt  16   else ret           ret    String format   c c c c           HexChars charAt  int    v  gt  gt  12   amp  0x0f            HexChars charAt  int    v  gt  gt   8   amp  0x0f            HexChars charAt  int    v  gt  gt   4   amp  0x0f            HexChars charAt  int    v         amp  0x0f         return ret     with replace char oldchar   char newchar   somewhat faster but pretty limited               ret     ABCD           replace  A   HexChars charAt  int    v  gt  gt  12   amp  0x0f             replace  B   HexChars charAt  int    v  gt  gt   8   amp  0x0f             replace  C   HexChars charAt  int    v  gt  gt   4   amp  0x0f             replace  D   HexChars charAt  int    v         amp  0x0f              There is a third solution consisting of just adding the char to ret one by one  char are numbers that add to each other   such as in       ret    HexChars charAt  int    v  gt  gt  12   amp  0x0f     ret    HexChars charAt  int    v  gt  gt   8   amp  0x0f               but that d be really ugly

[java] Sprintf equivalent in Java

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