Is there an equivalent for toPrecision() in Java?

Question

In porting an algorithm from JavaScript to Java, I've run into the problem that I need a replacement for JavaScript's toPrecision(). The problem is that I don't have a clue how small or large the numbers will be, so I can't use a simple NumberFormat with the right format. Is there a standard class that offers a similar functionality? EDIT Here is what I came up with: ``` double toPrecision(double n, double p) { if (n==0) return 0; double e = Math.floor(Math.log10(Math.abs(n))); double f = Math.exp((e-p+1)*Math.log(10)); return Math.round(n/f)*f; } ``` In principle, it does the right thing, but rounding errors completely ruin it. For example, `toPrecision(12.34567, 3)` returns `12.299999999999997` EDIT 2 This version works perfectly for 11 out of 12 test cases... ``` double toPrecision(double n, double p) { if (n==0) return 0; double e = Math.floor(Math.log10(Math.abs(n))); double f = Math.round(Math.exp((Math.abs(e-p+1))*Math.log(10))); if (e-p+1<0) { f = 1/f; } return Math.round(n/f)…

Accepted Answer

Use `BigDecimal` and `setScale()` method to set the precision

```
BigDecimal bd = new BigDecimal("1.23456789");
System.out.println(bd.setScale(3,BigDecimal.ROUND_HALF_UP));
```

Output

```
1.235
```

See

- IDEone demo

Is there an equivalent for toPrecision() in Java?

Solution

Problem