While some variables such as fields can be initialized and be assigned a default value, it is possible for local variables to not be initialized. This however is not a good practice as it is capable of critically altering your program's path, thereby affecting its logic.
It is therefore recommended that you always initialize variables, ideally where they're being declared.
// invalid: here `x` is uninitialized int x, y = 2;
int x = 1, y = 2;