How can I tell if a Java integer is null

Question

Greetings   I m trying to validate whether my integer is null   If it is  I need to prompt the user to enter a value   My background is Perl  so my first attempt looks like this   int startIn   Integer parseInt  startField getText      if  startIn         JOptionPane showMessageDialog null            You must enter a number between 0-16    Input Error            JOptionPane ERROR MESSAGE                       This does not work  since Java is expecting boolean logic     In Perl  I can use  exists  to check whether hash array elements contain data with    items     one    two    three      items        if  exists  items 0          print  Something in   items  n     else       print  Nothing in   items  n       Is there a way to this in Java   Thank you for your help   Jeremiah  P S  Perl exists info

User · Answer

I don t think you can use  exists  on an integer in Perl  only on collections  Can you give an example of what you mean in Perl which matches your example in Java      Given an expression that specifies a hash element or array element  returns true if the specified element in the hash or array has ever been initialized  even if the corresponding value is undefined    This indicates it only applies to hash or array elements

User · Answer

This should help   Integer startIn   null       optional below but a good practice  to prevent errors   boolean dontContinue   false  try     Integer parseInt  startField getText       catch  NumberFormatException e     e printStackTrace          in java   assigns a boolean in if statements oddly     Thus double equal must be used  So if startIn is null  display the message if  startIn    null      JOptionPane showMessageDialog null          You must enter a number between 0-16    Input Error          JOptionPane ERROR MESSAGE                                      again optional  if  dontContinue    true        Do-some-error-fix

User · Answer

parseInt   is just going to throw an exception if the parsing can t complete successfully  You can instead use Integers  the corresponding object type  which makes things a little bit cleaner  So you probably want something closer to   Integer s   null   try      s   Integer valueOf startField getText       catch  NumberFormatException e                if  s    null            Beware if you do decide to use parseInt    parseInt   doesn t support good internationalization  so you have to jump through even more hoops   try       NumberFormat nf   NumberFormat getIntegerInstance locale       nf setParseIntegerOnly true       nf setMaximumIntegerDigits 9      Or whatever you d like to max out at          Start parsing from the beginning      ParsePosition p   new ParsePosition 0        int val   format parse str  p  intValue        if  p getIndex      str length                 There s some stuff after all the digits are done being processed                Work with the processed value here    catch  java text ParseFormatException exc           Something blew up in the parsing

User · Answer

There is no exists for a SCALAR in Perl  anyway  The Perl way is   defined   x      and the equivalent Java is   anInteger    null   Those are the equivalents    exists  hash key    Is like the Java  map containsKey   key      From your example  I think you re looking for   if   startIn    null

User · Answer

For me just using the Integer toString   method works for me just fine   You can convert it over if you just want to very if it is null   Example below   private void setCarColor int redIn  int blueIn  int greenIn      Integer s   null  if  Integer toString redIn     null    Integer toString blueIn     null        Integer toString greenIn     null

User · Answer

ints are value types  they can never be null  Instead  if the parsing failed  parseInt will throw a NumberFormatException that you need to catch

User · Answer

Try this   Integer startIn   null   try     startIn   Integer valueOf startField getText       catch  NumberFormatException e                   if  startIn    null         Prompt for value

[java] How can I tell if a Java integer is null?

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