How to save the double value in a customized format, such as keeping 6 digits only

[cake naiyou]

In my code, the computation can generate double value in its standard long format, like 0.469696968793869

If I just want to save it in a shorter format with just six digits, like 0.469697, and use it for later computation. How to do that? Thanks.

[Piyush Joshi]

There can be many ways of doing this.

One of them is using DecimalFormat class:

double roundIt(double d){
		DecimalFormat def = new DecimalFormat("#.######");
		def.setRoundingMode(RoundingMode.HALF_UP);
		return Double.valueOf(def.format(d));
	}

[Rob Spoor]

Not really. This still has the problem that double and float are not precise; see item 20 in our Beginner's FAQ. The only data type in the Java API that can solve this issue is BigDecimal. Never instantiate one from a double though, use the String constructor instead:

BigDecimal original = new BigDecimal("0.469696968793869");
BigDecimal truncated = original.setScale(6, RoundingMode.HALF_UP);

[Riaan Nel]

If the format is only relevant when displaying the data, use DecimalFormat to get a formatted String representation of the double. The double value is just a number - it doesn't have a strict 'format' as such. As an example, 1.000000 and 1.0 are the exact same number.

If precision is important, use a BigDecimal instead of a double.

[Campbell Ritchie]

For displaying the number, it is far easier to use the %f tag. Details in the Java™ Tutorials and in the Formatter class documentation.