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.

Answer 1

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. } 

Answer 2

Try this:

Integer startIn = null;  try {   startIn = Integer.valueOf(startField.getText()); } catch (NumberFormatException e) {   .   .   . }  if (startIn == null) {   // Prompt for value... }