Consider the code if(x == null || x.size() == 0) { doSomething(); continue; } System.out.println(x.size()); Let us extract the variable x.size(). I get: int size = x.size(); if(x == null || size == 0) {... This obviously has different semantics when x is null. I don't see a semantics-preserving variant that would not cause code duplication of the 'then' clause, so I suggest to give out a warning dialog in such cases, or possibly to refuse doing such a dangerous 'refactoring' at all.