使用NumberFormat或DecimalFormat

Question

In most case, how can we justify, when shall we use

NumberFormat.getInstance();

When shall we use

new DecimalForamt(...);

Answer 1

If you want to specify how your numbers are formatted, then you must use the DecimalFormat constructor. If you want "the way most numbers are represented in my current locale", then use the default instance of NumberFormat.

Answer 2

NumberFormat.getInstance actually gets the formatter based on the locale and number style. It might actually return the DecimalFormat() object. "DecimalFormat is a concrete subclass of NumberFormat that formats decimal numbers" - From JDK javadocs

Answer 3

I had the same issue concerning locale. You can create a DecimalFormat object for a US locale by instantiating a NumberFormat and then casting it to a DecimalFormat. This is what Oracle says:

The preceding example created a DecimalFormat object for the default Locale. If you want a DecimalFormat object for a nondefault Locale, you instantiate a NumberFormat and then cast it to DecimalFormat. Here's an example:

NumberFormat nf = NumberFormat.getNumberInstance(loc);

DecimalFormat df = (DecimalFormat)nf;

df.applyPattern(pattern);

String output = df.format(value);

System.out.println(pattern + " " + output + " " + loc.toString());

https://docs.oracle.com/javase/tutorial/i18n/format/decimalFormat.html