Why do I get a “Possible null pointer dereference” warning?

问题

Why do FindBugs raises me the following warning: Possible null pointer dereference.

current = myService.getCategoryParent(current);
if (current != null) { // The warning appears here

I don't understand how testing a variable against null could dereference it.

回答1:

I suspect the error/warning is actually on the line above the line you've indicated.

//                   here ------------v
current = myService.getCategoryParent(current);
if (current != null) {

来源：https://stackoverflow.com/questions/10312399/why-do-i-get-a-possible-null-pointer-dereference-warning