java if() or statement issue

I have the following if() statement:

if (stringCharCheck(x, num) && xm1.equals("-") && (!stringCharCheck(xm2, num)||!xm2.equals("-")))

When I get rid of the or so either:

if (stringCharCheck(x, num) && xm1.equals("-") && !stringCharCheck(xm2, num))

or

if (stringCharCheck(x, num) && xm1.equals("-") && !xm2.equals("-"))

Everything works as intended. The stringCharCheck method is a boolean and I just want to say "if false or xm2 == "-" then do this...

I can't see what I am doing incorrectly.