double amount =200.0;
Locale locale = new Locale("en", "US");      
NumberFormat currencyFormatter = NumberFormat.getCurrencyInstance(locale);
System.out.println(currencyFormatter.format(amount));

or

double amount =200.0;
System.out.println(NumberFormat.getCurrencyInstance(new Locale("en", "US"))
        .format(amount));

The best way to display currency

Output

$200.00

Note: Locale constructors have been deprecated. See Obtaining a Locale for other options.

So, since Locale constructors are deprecated, we can use Locale.Builder() to construct a Locale object.

    double amount =200.0;
    Locale locale = new Locale.Builder().setLanguage("en").setRegion("US").build();
    NumberFormat currencyFormatter = NumberFormat.getCurrencyInstance(locale);
    System.out.println(currencyFormatter.format(amount));

or

    double amount =200.0;
    System.out.println(NumberFormat.getCurrencyInstance(new Locale.Builder().setLanguage("en").setRegion("US").build()).format(amount));

Output

$200.00

If you don't want to use sign use this method

double amount = 200;
DecimalFormat twoPlaces = new DecimalFormat("0.00");
System.out.println(twoPlaces.format(amount));

200.00

This also can be use (With the thousand separator )

double amount = 2000000;    
System.out.println(String.format("%,.2f", amount));          

2,000,000.00