Java IDEs Null Pointer Alerts

Question

Is there an IDE or IDE plugin that would alert the developer for a possible NPE? For example:

Object[] x = getMyObjects();

if (x.length > 0){

   // do my stuff

}

It would be nice if the IDE alerts that x is not checked for a possible null value. It would save many engineering hours..

Answer 1

My copy of Eclipse raises a warning for this by default.

Answer 2

in addition to John's answer...

---

Eclipse 3.4 gave me an excellent message, which was something like :

The variable can only be null at this point.

I couldn't believe it at first, but it was true. It was two expressions like :

if ((var == null) && (var.getProperty().equals("")) {

if ((var != null) || (var..getProperty().equals("")) {

Answer 3

This is something that FindBugs can detect among many other usefull things. There is also a Eclipse plugin available.

Answer 4

NullPointerExceptions are programming errors by nature.

What could you do if the given array is null? A. skip the check. A better alternative would be to return an empty array:

public Object [] getMyObjects() {
     /// do a lot of stuff 

    if( nothingToReturn() ){
        return new Object[0];
     } else {
         return nonNullArray;
     }
}

So

if( x.length > 0 ) 

Never throws Npe in first place.

Although It would be nice, very soon you'll realize your code will be unreadable.

That's why "encapsulation" is such an important concept in OOP ( that way other object's won't nullify your data ) .

I think it's fair to check if external classes return null or not ( which by the way should be well documented ) but for internal methods, the real problem is, the own object doesn't know the state of its own instance variables.

_{NOTE This was too large for a comment, that's why I provided a CW answer instead.}

Answer 5

You might want to start with adding the FindBugs plugin to check for this kind (and many more) bugs on every save. And if you haven't already, add the CheckStyle plugin too :-)

Answer 6

Eclipse 3.5 (and AFAIR 3.4, too) has two compiler options for Nullpointers.

You can find them at Window -> Preferences -> Java -> Compiler -> Error/Warnings -> Potential programming problems.

My preferred settings are Error for Null pointer access (these are definitly raising Exceptions) and Warning for the Potential null pointer access.