In C, I can write an if-statement
if (firstInt & 1)
but when I try and do the same in Java, the compiler tells me \"incompatible types\
In C an integer expression can be used implicitly as a boolean expression (although I would argue that it is a bad idea), where zero is false and any non-zero value is true.
In Java that is not allowed so you have to make the expression explicitly boolean by comparing the integer result to some other integer value or expression using a comparison operator.
Any of the following should work for you:
if ((firstInt & 1) != 0)
if ((firstInt & 1) > 0)
if ((firstInt & 1) == 1)