Processing 1.0 - Processing Discourse - RESOLVED::Testing for null

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RESOLVED::Testing for null (Read 435 times)

smhall05

RESOLVED::Testing for null
Jun 17^th, 2008, 12:09am

Is there a way to test for null? I have used the following in TCL and it works fine:

Code:


if {$some_variable != ""} { do something }

However in Processing, when null is "found" the NullPointerException is thrown. How would I test for null in the following example? Since Dog is not found in the first line the exception is thrown which I don't want. How do I prevent this behavior?

Code:


String lines[] = {"Elephants have truncks", "Cows produce milk", "Dogs bark", "Cat meow"};
String type_animal = new String();

for(int i = 0; i < lines.length; i++) {
  String type[] = match(lines[i], "(D\\w{3})");
  //println(type);
  type_animal = type[0];
  println(type_animal);
}

« Last Edit: Jun 17^th, 2008, 5:13am by smhall05 »

JohnG

Re: Testing for null
Reply #1 - Jun 17^th, 2008, 12:23am

Code:

 String lines[] = {"Elephants have truncks", "Cows produce milk", "Dogs bark", "Cat meow"};
String type_animal = new String();
 
for(int i = 0; i < lines.length; i++) {
  String type[] = match(lines[i], "(D\\w{3})");
  //println(type);
  //what you actually want to do is:
  if(type.length>0)
    type_animal = type[0];
  //however to answer your question
  if(type[0]!=null)
    type_animal = type[0];
  
  println(type_animal);
}

smhall05 YaBB Newbies Offline Posts: 13	UPDATE: Testing for null Reply #2 - Jun 17^th, 2008, 3:16am Thanks for the reply, however it seems like testing for null throws the NullPointerException. Any other ideas?

fry

Re: Testing for null
Reply #3 - Jun 17^th, 2008, 4:37am

match() returns null if there's no match, so you first have to check 'type' (the array), not 'type[0]' (an element in the array). really all you need is:

Code:


if (type != null) {
  type_animal = type[0];
}

there's no need to check type.length, because the entire match string is enclosed in parens. so either it matched, returning a 1 element array, or it didn't (and will return null).

(edit) and sorry the docs aren't very clear on this... they were written by a monkey who can't write english. (me cramming it in while preparing a release.)

smhall05 YaBB Newbies Offline Posts: 13	Re: Testing for null Reply #4 - Jun 17^th, 2008, 4:57am Perfect!

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