How do I convert from int to String

Question

I m working on a project where all conversions from int to String are done like this   int i   5  String strI        i    I m not familiar with Java    Is this usual practice or is something wrong  as I suppose

User · Answer

It s not a good way   When doing conversion from int to string  this should be used   int i   5  String strI   String valueOf i

User · Answer

Personally  I don t see anything bad in this code   It s pretty useful when you want to log an int value  and the logger just accepts a string  I would say such a conversion is convenient when you need to call a method accepting a String  but you have an int value   As for the choice between Integer toString or String valueOf  it s all a matter of taste     And internally  the String valueOf calls the Integer toString method by the way

User · Answer

String strI   String valueOf i    String string   Integer toString i     Both of the ways are correct

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A lot of introductory University courses seem to teach this style  for two reasons  in my experience     It doesn   t require understanding of classes or methods  Usually  this is taught way before the word    class    is ever mentioned     nor even method calls  So using something like String valueOf      would confuse students  It is an illustration of    operator overloading        in fact  this was sold to us as the idiomatic overloaded operator  small wonder here  since Java doesn   t allow custom operator overloading     So it may either be born out of didactic necessity  although I   d argue that this is just bad teaching  or be used to illustrate a principle that   s otherwise quite hard to demonstrate in Java

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It s not only the optimization1  I don t like       i   because it does not express what I really want to do 2   I don t want to append an integer to an  empty  string  I want to convert an integer to string   Integer toString i    Or  not my prefered  but still better than concatenation  get a string representation of an object  integer    String valueOf i    1  For code that is called very often  like in loops  optimization sure is also a point for not using concatenation   2  this is not valid for use of real concatenation like in System out println  Index      i   or String id    ID    i

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Normal ways would be Integer toString i  or String valueOf i    The concatenation will work  but it is unconventional and could be a bad smell as it suggests the author doesn t know about the two methods above  what else might they not know     Java has special support for the   operator when used with strings  see the documentation  which translates the code you posted into   StringBuilder sb   new StringBuilder    sb append      sb append i   String strI   sb toString      at compile-time  It s slightly less efficient  sb append   ends up calling Integer getChars    which is what Integer toString   would ve done anyway   but it works   To answer Grodriguez s comment     No  the compiler doesn t optimise out the empty string in this case - look   simon lucifer    cat TestClass java public class TestClass     public static void main String   args        int i   5      String strI        i        simon lucifer    javac TestClass java  amp  amp  javap -c TestClass Compiled from  TestClass java  public class TestClass extends java lang Object  public TestClass      Code     0     aload 0    1     invokespecial     1    Method java lang Object   lt init gt     V    4     return  public static void main java lang String       Code     0     iconst 5    1     istore 1   Initialise the StringBuilder      2     new     2    class java lang StringBuilder    5     dup    6     invokespecial     3    Method java lang StringBuilder   lt init gt     V   Append the empty string      9     ldc     4    String    11     invokevirtual     5    Method java lang StringBuilder append   Ljava lang String  Ljava lang StringBuilder    Append the integer      14     iload 1    15     invokevirtual     6    Method java lang StringBuilder append   I Ljava lang StringBuilder    Extract the final string      18     invokevirtual     7    Method java lang StringBuilder toString    Ljava lang String     21     astore 2    22     return     There s a proposal and ongoing work to change this behaviour  targetted for JDK nbsp 9

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There are various ways of converting to Strings   StringBuilder string   string append i  toString    String string   String valueOf i   String string   Integer toString i

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Personally I think that      i does look as the original question poster states  smelly   I have used a lot of OO languages besides Java  If that syntax was intended to be appropriate then Java would just interpret the i alone without needing the    as desired to be converted to a string and do it since the destination type is unambiguous and only a single value would be being supplied on the right  The other seems like a  trick  to fool the compiler  bad mojo when different versions of Javac made by other manufacturers or from other platforms are considered if the code ever needs to be ported  Heck for my money it should like many other OOL s just take a Typecast   String  i  winks  Given my way of learning and for ease of understanding such a construct when reading others code quickly I vote for the Integer toString i  method  Forgetting a ns or two in how Java implements things in the background vs  String valueOf i  this method feels right to me and says exactly what is happening  I have and Integer and I wish it converted to a String   A good point made a couple times is perhaps just using StringBuilder up front is a good answer to building Strings mixed of text and ints or other objects since thats what will be used in the background anyways right   Just my two cents thrown into the already well paid kitty of the answers to the Mans question    smiles  EDIT TO MY OWN ANSWER AFTER SOME REFLECTION   Ok  Ok  I was thinking on this some more and String valueOf i  is also perfectly good as well it says  I want a String that represents the value of an Integer  lol  English is by far more difficult to parse then Java  But  I leave the rest of my answer comment    I was always taught to use the lowest level of a method function chain if possible and still maintains readablity so if String valueOf calls Integer toString then Why use a whole orange if your just gonna peel it anyways  Hmmm   To clarify my comment about StringBuilder  I build a lot of strings with combos of mostly literal text and int s and they wind up being long and ugly with calls to the above mentioned routines imbedded between the   s  so seems to me if those become SB objects anyways and the append method has overloads it might be cleaner to just go ahead and use it    So I guess I am up to 5 cents on this one now  eh  lol

User · Answer

use Integer toString tmpInt  trim

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The expression        i   leads to string conversion of i at runtime  The overall type of the expression is String  i is first converted to an Integer object  new Integer i    then String valueOf Object obj  is called  So it is equivalent to       String valueOf new Integer i      Obviously  this is slightly less performant than just calling String valueOf new Integer i   which will produce the very same result   The advantage of    i is that typing is easier faster and some people might think  that it s easier to read  It is not a code smell as it does not indicate any deeper problem    Reference  JLS 15 8 1

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Using      i is the shortest and simplest way to convert a number to a string   It is not the most efficient  but it is the clearest IMHO and that is usually more important   The simpler the code  the less likely you are to make a mistake

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It s acceptable  but I ve never written anything like that   I d prefer this    String strI   Integer toString i

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This technique was taught in an undergraduate level introduction-to-Java class I took over a decade ago  However  I should note that  IIRC  we hadn t yet gotten to the String and Integer class methods   The technique is simple and quick to type  If all I m doing is printing something  I ll use it  for example  System out println      i    However  I think it s not the best way to do a conversion  as it takes a second of thought to realize what s going on when it s being used this way  Also  if performance is a concern  it seems slower  more below  as well as in other answers    Personally  I prefer Integer toString    as it is obvious what s happening  String valueOf   would be my second choice  as it seems to be confusing  witness the comments after darioo s answer    Just for grins    I wrote up classes to test the three techniques        i   Integer toString  and String ValueOf  Each test just converted the ints from 1 to 10000 to Strings  I then ran each through the Linux time command five times  Integer toString   was slightly faster than String valueOf   once  they tied three times  and String valueOf   was faster once  however  the difference was never more than a couple of milliseconds   The      i technique was slower than both on every test except one  when it was 1 millisecond faster than Integer toString   and 1 millisecond slower than String valueOf    obviously on the same test where String valueOf   was faster than Integer toString     While it was usually only a couple milliseconds slower  there was one test where it was about 50 milliseconds slower  YMMV

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As already pointed out Integer toString   or String valueOf   are the way to go  I was curious and did a quick benchmark  Integer toString i  and String valueOf i  are basically identical in performance  with Integer toString i  being a tiny bit faster  However i    quot  quot  is 1 7 times slower  import java util Random   public class Test        public static void main String   args            long concat   0          long valueOf   0          long toString   0                   int iterations   10000          int runs   1000          for int i   0  i  lt  runs  i                  concat    concat iterations               valueOf    valueOf iterations               toString    to String iterations                              System out println  quot concat   quot    concat runs           System out println  quot valueOf   quot    valueOf runs           System out println  quot toString   quot    toString runs                  public static long concat int iterations            Random r   new Random 0           long start   System nanoTime            for int i   0  i  lt  iterations  i                  String s   r nextInt      quot  quot                     return System nanoTime   - start                 public static long valueOf int iterations            Random r   new Random 0           long start   System nanoTime            for int i   0  i  lt  iterations  i                  String s   String valueOf r nextInt                       return System nanoTime   - start                 public static long to String int iterations            Random r   new Random 0           long start   System nanoTime            for int i   0  i  lt  iterations  i                  String s   Integer toString r nextInt                       return System nanoTime   - start           Output  concat  1004109 valueOf  590978 toString  587236

User · Answer

It depends on how you want to use your String  This can help   String total    Integer toString 123    Double toString 456 789

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There are three ways of converting to Strings   String string        i  String string   String valueOf i   String string   Integer toString i

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Try simple typecasting  char c    char  i

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The other way I am aware of is from the Integer class   Integer toString int n   Integer toString int n  int radix     A concrete example  though I wouldn t think you need any    String five   Integer toString 5      returns  5    It also works for other primitive types  for instance Double toString   See here for more details

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There are many way to convert an integer to a string   1   Integer toString 10     2    String hundred   String valueOf 100      You can pass an int constant  int ten   10   String ten   String valueOf ten    3   String thousand        1000     String concatenation   4   String million   String format   d   1000000

User · Answer

Mostly ditto on SimonJ  I really dislike the    i idiom  If you say String valueOf i   Java converts the integer to a string and returns the result  If you say    i  Java creates a StringBuilder object  appends an empty string to it  converts the integer to a string  appends this to the StringBuilder  then converts the StringBuilder to a String  That s a lot of extra steps  I suppose if you do it once in a big program  it s no big deal  But if you re doing this all the time  you re making the computer do a bunch of extra work and creating all these extra objects that then have to be cleaned up  I don t want to get fanatic about micro-optimization  but I don t want to be pointlessly wasteful either

[java] How do I convert from int to String?

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