if(x!=y) vs if(x==y)

Question

I have run the PMD plugin in Eclipse against my code and I'm getting a high priority warning for code similar to the one shown below:

 if(singleRequest !=null){    // do my work  }else{    // do my other work  } 

PMD says `Avoid if (x != y) ..; else ..;

And the description of the error looks like this:

In an "if" expression with an "else" clause, avoid negation in the test.  For example, rephrase: if (x != y) diff(); else same(); as: if (x == y) same(); else diff(); Most "if (x != y)" cases without an "else" are often return 

but I still can't understand the impact on my code. If someone could guide me with an example, I would appreciate it.