Java DecimalFormat.format does not format the number?

Question

I have the method below, but for some reason it is not formatting the area to have only one decimal. All help is appreciated.

public double beraknaArea()
    {
       DecimalFormat formatter = new DecimalFormat("#0.0");
       double area = 0;
       area = radie*radie*3.14;
       formatter.format(area);
       return area;
     }

Answer 1

You are returning the same double, and not the output of the formatter.

The format() method does not alter the double that you pass in, it returns a String format of the double.

Answer 2

No methods in Java may change the type of a declared variable, or mutate any primitive value (or indeed String). You need to return what formatter.format(area) returns, not the unchanged value of area.

public String beraknaArea()
{
   DecimalFormat formatter = new DecimalFormat("#0.0");
   double area = radie*radie*3.14;
   return formatter.format(area);
 }