Good way to encapsulate Integer parseInt

Question

I have a project in which we often use Integer parseInt   to convert a String to an int  When something goes wrong  for example  the String is not a number but the letter a  or whatever  this method will throw an exception  However  if I have to handle exceptions in my code everywhere  this starts to look very ugly very quickly  I would like to put this in a method  however  I have no clue how to return a clean value in order to show that the conversion went wrong    In C   I could have created a method that accepted a pointer to an int and let the method itself return true or false  However  as far as I know  this is not possible in Java  I could also create an object that contains a true false variable and the converted value  but this does not seem ideal either  The same thing goes for a global value  and this might give me some trouble with multithreading    So is there a clean way to do this

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You could roll your own  but it s just as easy to use commons lang s StringUtils isNumeric   method  It uses Character isDigit   to iterate over each character in the String

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You could return an Integer instead of an int  returning null on parse failure   It s a shame Java doesn t provide a way of doing this without there being an exception thrown internally though - you can hide the exception  by catching it and returning null   but it could still be a performance issue if you re parsing hundreds of thousands of bits of user-provided data   EDIT  Code for such a method   public static Integer tryParse String text      try       return Integer parseInt text       catch  NumberFormatException e        return null          Note that I m not sure off the top of my head what this will do if text is null  You should consider that - if it represents a bug  i e  your code may well pass an invalid value  but should never pass null  then throwing an exception is appropriate  if it doesn t represent a bug then you should probably just return null as you would for any other invalid value   Originally this answer used the new Integer String  constructor  it now uses Integer parseInt and a boxing operation  in this way small values will end up being boxed to cached Integer objects  making it more efficient in those situations

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You could also replicate the C   behaviour that you want very simply  public static boolean parseInt String str  int   byRef        if byRef  null  return false      try          byRef 0    Integer parseInt prop          return true        catch  NumberFormatException ex           return false            You would use the method like so   int   byRef   new int 1   boolean result   parseInt  123  byRef     After that the variable result it s true if everything went allright and byRef 0  contains the parsed value   Personally  I would stick to catching the exception

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What behaviour do you expect when it s not a number   If  for example  you often have a default value to use when the input is not a number  then a method such as this could be useful   public static int parseWithDefault String number  int defaultVal      try       return Integer parseInt number       catch  NumberFormatException e        return defaultVal          Similar methods can be written for different default behaviour when the input can t be parsed

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They way I handle this problem is recursively  For example when reading data from the console   Java util Scanner keyboard   new Java util Scanner System in    public int GetMyInt        int ret      System out print  Give me an Int          try          ret   Integer parseInt keyboard NextLine                catch Exception e           System out println   nThere was an error try again  n            ret   GetMyInt              return ret

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In some cases you should handle parsing errors as fail-fast situations  but in others cases  such as application configuration  I prefer to handle missing input with default values using Apache Commons Lang 3 NumberUtils   int port   NumberUtils toInt properties getProperty  port    8080

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I would like to throw in another proposal that works if one specifically requests integers  Simply use long and use Long MIN VALUE for error cases  This is similar to the approach that is used for chars in Reader where Reader read   returns an integer in the range of a char or -1 if the reader is empty   For Float and Double  NaN can be used in a similar way   public static long parseInteger String s        try           return Integer parseInt s         catch  NumberFormatException e            return Long MIN VALUE                   long l   parseInteger  ABC    if  l    Long MIN VALUE               error   else       int i    int  l

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I would suggest you consider a method like   IntegerUtilities isValidInteger String s    which you then implement as you see fit   If you want the result carried back - perhaps because you use Integer parseInt   anyway - you can use the array trick    IntegerUtilities isValidInteger String s  int   result    where you set result 0  to the integer value found in the process

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There is Ints tryParse   in Guava  It doesn t throw exception on non-numeric string  however it does throw exception on null string

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Try with regular expression and default parameters argument  public static int parseIntWithDefault String str  int defaultInt        return str matches  -   d      Integer parseInt str    defaultInt      int testId   parseIntWithDefault  1001   0   System out print testId      1001  int testId   parseIntWithDefault  test1001   0   System out print testId      1001  int testId   parseIntWithDefault  -1001   0   System out print testId      -1001  int testId   parseIntWithDefault  test   0   System out print testId      0   if you re using apache commons lang3 then by using NumberUtils   int testId   NumberUtils toInt  test   0   System out print testId      0

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You can use a Null-Object like so   public class Convert         SuppressWarnings   UnnecessaryBoxing        public static final Integer NULL   new Integer 0        public static Integer convert String integer             try               return Integer valueOf integer             catch  NumberFormatException e                return NULL                        public static void main String   args             Integer a   convert  123            System out println  a equals 123        a equals 123            System out println  a    NULL      a    NULL             Integer b   convert  onetwothree            System out println  b equals 123        b equals 123            System out println  b    NULL      b    NULL             Integer c   convert  0            System out println  equals 0        c equals 0            System out println  c    NULL      c    NULL                The result of main in this example is   a equals 123    true a    NULL false b equals 123    false b    NULL true c equals 0    true c    NULL false   This way you can always test for failed conversion but still work with the results as Integer instances  You might also want to tweak the number NULL represents    0

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You shouldn t use Exceptions to validate your values   For single character there is a simple solution   Character isDigit     For longer values it s better to use some utils  NumberUtils provided by Apache would work perfectly here   NumberUtils isNumber     Please check https   commons apache org proper commons-lang javadocs api-2 6 org apache commons lang math NumberUtils html

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Considering existing answers  I ve copy-pasted and enhanced source code of Integer parseInt to do the job  and my solution   does not use potentially slow try-catch  unlike Lang 3 NumberUtils   does not use regexps which can t catch too big numbers  avoids boxing  unlike Guava s Ints tryParse     does not require any allocations  unlike int    Box  OptionalInt   accepts any CharSequence or a part of it instead of a whole String  can use any radix which Integer parseInt can  i e   2 36   does not depend on any libraries    The only downside is that there s no difference between toIntOfDefault  -1   -1  and toIntOrDefault  oops   -1    public static int toIntOrDefault CharSequence s  int def        return toIntOrDefault0 s  0  s length    10  def     public static int toIntOrDefault CharSequence s  int def  int radix        radixCheck radix       return toIntOrDefault0 s  0  s length    radix  def     public static int toIntOrDefault CharSequence s  int start  int endExclusive  int def        boundsCheck start  endExclusive  s length         return toIntOrDefault0 s  start  endExclusive  10  def     public static int toIntOrDefault CharSequence s  int start  int endExclusive  int radix  int def        radixCheck radix       boundsCheck start  endExclusive  s length         return toIntOrDefault0 s  start  endExclusive  radix  def     private static int toIntOrDefault0 CharSequence s  int start  int endExclusive  int radix  int def        if  start    endExclusive  return def     empty      boolean negative   false      int limit   -Integer MAX VALUE       char firstChar   s charAt start       if  firstChar  lt   0        Possible leading     or  -          if  firstChar     -                 negative   true              limit   Integer MIN VALUE            else if  firstChar                       return def                     start               Cannot have lone     or  -          if  start    endExclusive  return def            int multmin   limit   radix      int result   0      while  start  lt  endExclusive               Accumulating negatively avoids surprises near MAX VALUE         int digit   Character digit s charAt start     radix           if  digit  lt  0    result  lt  multmin  return def          result    radix          if  result  lt  limit   digit  return def          result -  digit            return negative   result   -result    private static void radixCheck int radix        if  radix  lt  Character MIN RADIX    radix  gt  Character MAX RADIX          throw new NumberFormatException                   radix     radix             Character MIN RADIX         Character MAX RADIX           private static void boundsCheck int start  int endExclusive  int len        if  start  lt  0    start  gt  len    start  gt  endExclusive          throw new IndexOutOfBoundsException  start     start        0  min     len          endExclusive              if  endExclusive  gt  len          throw new IndexOutOfBoundsException  endExclusive     endExclusive      gt  s length     len

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May be you can use something like this   public class Test   public interface Option lt T gt        T get         T getOrElse T def        boolean hasValue       final static class Some lt T gt  implements Option lt T gt         private final T value       public Some T value            this value   value              Override     public T get             return value              Override     public T getOrElse T def            return value              Override     public boolean hasValue             return true           final static class None lt T gt  implements Option lt T gt          Override     public T get             throw new UnsupportedOperationException                Override     public T getOrElse T def            return def              Override     public boolean hasValue             return false            public static Option lt Integer gt  parseInt String s        Option lt Integer gt  result   new None lt Integer gt         try           Integer value   Integer parseInt s           result   new Some lt Integer gt  value         catch  NumberFormatException e              return result

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To avoid an exception  you can use Java s Format parseObject method  The code below is basically a simplified version of Apache Common s IntegerValidator class   public static boolean tryParse String s  int   result        NumberFormat format   NumberFormat getIntegerInstance        ParsePosition position   new ParsePosition 0       Object parsedValue   format parseObject s  position        if  position getErrorIndex    gt  -1                return false             if  position getIndex    lt  s length                  return false             result 0      Long  parsedValue  intValue        return true      You can either use AtomicInteger or the int   array trick depending upon your preference   Here is my test that uses it -  int   i   new int 1   Assert assertTrue IntUtils tryParse  123   i    Assert assertEquals 123  i 0

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What about forking the parseInt method   It s easy  just copy-paste the contents to a new utility that returns Integer or Optional lt Integer gt  and replace throws with returns  It seems there are no exceptions in the underlying code  but better check   By skipping the whole exception handling stuff  you can save some time on invalid inputs  And the method is there since JDK 1 0  so it is not likely you will have to do much to keep it up-to-date

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After reading the answers to the question I think encapsulating or wrapping the parseInt method is not necessary  maybe even not a good idea   You could return  null  as Jon suggested  but that s more or less replacing a try catch construct by a null-check  There s just a slight difference on the behaviour if you  forget  error handling  if you don t catch the exception  there s no assignment and the left hand side variable keeps it old value  If you don t test for null  you ll probably get hit by the JVM  NPE    yawn s suggestion looks more elegant to me  because I do not like returning null to signal some errors or exceptional states  Now you have to check referential equality with a predefined object  that indicates a problem  But  as others argue  if again you  forget  to check and a String is unparsable  the program continous with the wrapped int inside your  ERROR  or  NULL  object   Nikolay s solution is even more object orientated and will work with parseXXX methods from other wrapper classes aswell  But in the end  he just replaced the NumberFormatException by an OperationNotSupported exception - again you need a try catch to handle unparsable inputs   So  its my conclusion to not encapsulate the plain parseInt method  I d only encapsulate if I could add some  application depended  error handling as well

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To avoid handling exceptions use a regular expression to make sure you have all digits first     Checking for Regular expression that matches digits if value matches    d            Integer parseInt value

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My Java is a little rusty  but let me see if I can point you in the right direction   public class Converter        public static Integer parseInt String str            Integer n   null           try               n   new Integer Integer tryParse str              catch  NumberFormatException ex                   leave n null  the string is invalid                    return n             If your return value is null  you have a bad value  Otherwise  you have a valid Integer

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This is somewhat similar to Nikolay s solution    private static class Box lt T gt      T me    public Box        public T get     return me      public void set T fromParse    me   fromParse         private interface Parser lt T gt      public void setExclusion String regex     public boolean isExcluded String s     public T parse String s        public static  lt T gt  boolean parser Box lt T gt  ref  Parser lt T gt  p  String toParse      if   p isExcluded toParse        ref set p parse toParse       return true      else return false       public static void main String args        Box lt Integer gt  a   new Box lt Integer gt       Parser lt Integer gt  intParser   new Parser lt Integer gt         String myExclusion     public void setExclusion String regex        myExclusion   regex          public boolean isExcluded String s        return s matches myExclusion           public Integer parse String s        return new Integer s               intParser setExclusion    D       if  parser a intParser  123    System out println a get       if   parser a intParser  abc    System out println  didn t parse   a get          The main method demos the code   Another way to implement the Parser interface would obviously be to just set   D   from construction  and have the methods do nothing

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I was also having the same problem  This is a method I wrote to ask the user for an input and not accept the input unless its an integer  Please note that I am a beginner so if the code is not working as expected  blame my inexperience    private int numberValue String value  boolean val  throws IOException         prints the value passed by the code implementer     System out println value         returns 0 is val is passed as false     Object num   0      while  val            num   br readLine            try               Integer numVal   Integer parseInt  String  num               if  numVal instanceof Integer                    val   false                  num   numVal                          catch  Exception e                System out println  Error  Please input a valid number  -                        return   Integer  num  intValue

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This is an answer to question 8391979   Does java have a int tryparse that doesn t throw an exception for bad data   duplicate   which is closed and linked to this question   Edit 2016 08 17  Added ltrimZeroes methods and called them in tryParse    Without leading zeroes in numberString may give false results  see comments in code   There is now also public static String ltrimZeroes String numberString  method which works for positive and negative  numbers  END Edit   Below you find a rudimentary Wrapper  boxing  class for int with an highly speed optimized tryParse   method  similar as in C   which parses the string itself and is a little bit faster than Integer parseInt String s  from Java   public class IntBoxSimple          IntBoxSimple - Rudimentary class to implement a C -like tryParse   method for int        A full blown IntBox class implementation can be found in my Github project        Copyright  c  2016  Peter Sulzer  F  rth        Program is published under the GNU General Public License  GPL  Version 1 or newer      protected int  n     this  boxes  the int value         BEGIN The following statements are only executed at the        first instantiation of an IntBox  i  e  only once  or        already compiled into the code at compile time      public static final int MAX INT LEN               String valueOf Integer MAX VALUE  length        public static final int MIN INT LEN               String valueOf Integer MIN VALUE  length        public static final int MAX INT LASTDEC               Integer parseInt String valueOf Integer MAX VALUE  substring 1        public static final int MAX INT FIRSTDIGIT               Integer parseInt String valueOf Integer MAX VALUE  substring 0  1        public static final int MIN INT LASTDEC               -Integer parseInt String valueOf Integer MIN VALUE  substring 2        public static final int MIN INT FIRSTDIGIT               Integer parseInt String valueOf Integer MIN VALUE  substring 1 2           END The following statements            ltrimZeroes   methods added 2016 08 16  are required by tryParse   methods      public static String ltrimZeroes String s            if  s charAt 0      -               return ltrimZeroesNegative s           else             return ltrimZeroesPositive s             protected static String ltrimZeroesNegative String s            int i 1          for     s charAt i      0   i             return   -  s substring i              protected static String ltrimZeroesPositive String s            int i 0          for     s charAt i      0   i             return  s substring i               public static boolean tryParse String s IntBoxSimple intBox            if  intBox    null                 intBoxSimple new IntBoxSimple       This doesn t work  as                intBoxSimple itself is passed by value and cannot changed                for the caller  I  e   out -arguments of C  cannot be simulated in Java              return false     so we simply return false         s s trim       leading and trailing whitespace is allowed for String s         int len s length            int rslt 0  d  dfirst 0  i  j          char c s charAt 0           if  c     -                 if  len  gt  MIN INT LEN       corrected  added  2016 08 17                 s   ltrimZeroesNegative s                   len   s length                              if  len  gt   MIN INT LEN                    c   s charAt 1                   if   Character isDigit c                       return false                  dfirst   c- 0                   if  len  gt  MIN INT LEN    dfirst  gt  MIN INT FIRSTDIGIT                      return false                            for  i   len - 1  j   1  i  gt   2  --i  j    10                    c   s charAt i                   if   Character isDigit c                       return false                  rslt -   c- 0   j                            if  len  lt  MIN INT LEN                    c   s charAt i                   if   Character isDigit c                       return false                  rslt -   c- 0   j                else                   if  dfirst  gt   MIN INT FIRSTDIGIT  amp  amp  rslt  lt  MIN INT LASTDEC                      return false                  rslt -  dfirst   j                          else               if  len  gt  MAX INT LEN       corrected  added  2016 08 16                 s   ltrimZeroesPositive s                   len s length                              if  len  gt   MAX INT LEN                    c   s charAt 0                   if   Character isDigit c                       return false                  dfirst   c- 0                   if  len  gt  MAX INT LEN    dfirst  gt  MAX INT FIRSTDIGIT                      return false                            for  i   len - 1  j   1  i  gt   1  --i  j    10                    c   s charAt i                   if   Character isDigit c                       return false                  rslt     c- 0   j                            if  len  lt  MAX INT LEN                    c   s charAt i                   if   Character isDigit c                       return false                  rslt     c- 0   j                            if  dfirst  gt   MAX INT FIRSTDIGIT  amp  amp  rslt  gt  MAX INT LASTDEC                  return false              rslt    dfirst j                    intBox  n rslt          return true                Get the value stored in an IntBoxSimple      public int get n             return  n            public int v        alternative shorter version  v for  value          return  n               Make objects of IntBoxSimple  needed as constructors are not public       public static IntBoxSimple makeIntBoxSimple             return new IntBoxSimple              public static IntBoxSimple makeIntBoxSimple int integerNumber            return new IntBoxSimple integerNumber                 constructors are not public         protected IntBoxSimple                 n 0     default value an IntBoxSimple holds           protected IntBoxSimple int integerNumber             n integerNumber            Test example program for class IntBoxSimple   import java io BufferedReader  import java io IOException  import java io InputStreamReader  public class IntBoxSimpleTest       public static void main  String args              IntBoxSimple ibs   IntBoxSimple makeIntBoxSimple            String in   null          BufferedReader br   new BufferedReader new InputStreamReader System in            do               System out printf                       Enter an integer number in the range  d to  d  n                           Integer MIN VALUE  Integer MAX VALUE               try   in   br readLine      catch  IOException ex               while   IntBoxSimple tryParse in  ibs            System out printf  The number you have entered was   d n   ibs v

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If you re using Java 8 or up  you can use a library I just released  https   github com robtimus try-parse  It has support for int  long and boolean that doesn t rely on catching exceptions  Unlike Guava s Ints tryParse it returns OptionalInt   OptionalLong   Optional  much like in https   stackoverflow com a 38451745 1180351 but more efficient

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The answer given by Jon Skeet is fine  but I don t like giving back a null Integer object  I find this confusing to use  Since Java 8 there is a better option  in my opinion   using the OptionalInt   public static OptionalInt tryParse String value     try        return OptionalInt of Integer parseInt value        catch  NumberFormatException e         return OptionalInt empty            This makes it explicit that you have to handle the case where no value is available  I would prefer if this kind of function would be added to the java library in the future  but I don t know if that will ever happen

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Maybe someone is looking for a more generic approach  since Java 8 there is the Package java util function that allows to define Supplier Functions  You could have a function that takes a supplier and a default value as follows  public static  lt T gt  T tryGetOrDefault Supplier lt T gt  supplier  T defaultValue        try           return supplier get          catch  Exception e            return defaultValue           With this function  you can execute any parsing method or even other methods that could throw an Exception while ensuring that no Exception can ever be thrown  Integer i   tryGetOrDefault    - gt  Integer parseInt stringValue   0   Long l   tryGetOrDefault    - gt  Long parseLong stringValue   0l   Double d   tryGetOrDefault    - gt  Double parseDouble stringValue   0d

[java] Good way to encapsulate Integer.parseInt()

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