# Round a double to 2 decimal places

###### Posted By: Anonymous

If the value is `200.3456`

, it should be formatted to `200.34`

.

If it is `200`

, then it should be `200.00`

.

## Solution

Here’s an utility that **rounds** (instead of *truncating*) a double to specified number of decimal places.

For example:

```
round(200.3456, 2); // returns 200.35
```

# Original version; watch out with this

```
public static double round(double value, int places) {
if (places < 0) throw new IllegalArgumentException();
long factor = (long) Math.pow(10, places);
value = value * factor;
long tmp = Math.round(value);
return (double) tmp / factor;
}
```

This **breaks down badly** in corner cases with either a very high number of decimal places (e.g. `round(1000.0d, 17)`

) or large integer part (e.g. `round(90080070060.1d, 9)`

). Thanks to Sloin for pointing this out.

I’ve been using the above to round “not-too-big” doubles to 2 or 3 decimal places happily for years (for example to clean up time in seconds for logging purposes: 27.987654321987 -> 27.99). But I guess it’s best to avoid it, since more reliable ways are readily available, with cleaner code too.

# So, use this instead

(Adapted from this answer by Louis Wasserman and this one by Sean Owen.)

```
public static double round(double value, int places) {
if (places < 0) throw new IllegalArgumentException();
BigDecimal bd = BigDecimal.valueOf(value);
bd = bd.setScale(places, RoundingMode.HALF_UP);
return bd.doubleValue();
}
```

Note that `HALF_UP`

is the rounding mode “commonly taught at school”. Peruse the RoundingMode documentation, if you suspect you need something else such as Bankers’ Rounding.

Of course, if you prefer, you can inline the above into a one-liner:

`new BigDecimal(value).setScale(places, RoundingMode.HALF_UP).doubleValue()`

# And in every case

Always remember that floating point representations using `float`

and `double`

are *inexact*.

For example, consider these expressions:

```
999199.1231231235 == 999199.1231231236 // true
1.03 - 0.41 // 0.6200000000000001
```

**For exactness, you want to use BigDecimal**. And while at it, use the constructor that takes a String, never the one taking double. For instance, try executing this:

```
System.out.println(new BigDecimal(1.03).subtract(new BigDecimal(0.41)));
System.out.println(new BigDecimal("1.03").subtract(new BigDecimal("0.41")));
```

Some excellent further reading on the topic:

- Item 48: “Avoid
`float`

and`double`

if exact answers are required” in*Effective Java*(2nd ed) by Joshua Bloch - What Every Programmer Should Know About Floating-Point Arithmetic

If you wanted String *formatting* instead of (or in addition to) strictly rounding numbers, see the other answers.

Specifically, note that `round(200, 0)`

returns `200.0`

. If you want to output “**200.00**“, you should first round and then format the result for output (which is perfectly explained in Jesper’s answer).

###### Answered By: Anonymous

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