Checking the "boolean" result of an "int" type

Why not use the boolean type ? That will work as you expect without the potentially problematic integer/boolean conflation.

private boolean isValid;
...
if (!isValid) {
   ...
}

Note that this is the idiomatic Java approach. 3rd party libs use this, and consumers of your API will use and expect it too. I would expect libs that you use to give you booleans, and as such it's just you treating ints as booleans.

Try BooleanUtils from Apache common-lang.

  BooleanUtils.toBoolean(0) = Boolean.FALSE
  BooleanUtils.toBoolean(1) = Boolean.TRUE
  BooleanUtils.toBoolean(2) = Boolean.TRUE

In Java,

if ( i != 0 )

is the idiomatic way to check whether the integer i differs from zero.

If i is used as a flag, it should be of type boolean and not of type int.