Types and casting

In Java you set each variable's type when you declare it, and that type never changes: int for whole numbers, double for decimals, boolean for true or false, char for a single character written between single quotes like 'A', and String for text written between double quotes. The largest value an int can hold is about 2.1 billion, so when you need more, use long and put the letter L after the number: 3_000_000_000L.

The first trap is that dividing an integer by an integer gives an integer and drops the fraction, so 47 / 6 is 7. Storing the result in a double doesn't bring the fraction back, because it was already lost, so cast one side before dividing: (double) kills / deaths. The same trap shows up in multiplication: players * xpEach is computed as an int, so it overflows and turns negative before it ever reaches the long. Write (long) players * xpEach instead.

(int) 30.83 drops the fraction and gives 30, while Math.round(30.83) rounds to 31. But Math.round returns a long, and Java won't turn it into an int on its own, so write (int) Math.round(x). To round to two decimal places, write Math.round(x * 100) / 100.0, and don't drop the .0, or the division becomes integer division again.