Rounding has unexpected results in Java

Question

I was surprised when I run this code:

int  x = (int)4.9f;
System.out.println(x);

Why is the result 4 and not 5?

Answer 1

It's because you're not rounding, but casting a float as integer. Casting simply removes the decimal part. If you want to round, you must use

double x = 4.9f;
System.out.println(Math.round(x));

Also, if you want to use explicit upper or lower rounding, you should use Math.ceil(x) or Math.floor(x) instead.

Answer 2

Using a cast simply truncates the value rather than performing proper rounding. You can use Math.round to get a correctly rounded value, or BigDecimal for a choice of 8 different rounding modes.

Answer 3

When (int)4.9f is used, it will simply truncate the decimal values (no rounding!). For rounding, you need to use Math.round() function.

Answer 4

You are using an int and int cant hold decimal numbers as you are casting a float to int so it removes the digit after the decimal..

int  x = (int)4.9f;
System.out.println(x);

So use

double x = 4.9f