显示数组时如何使用DecimalFormat？

Question

I'm writing a cash register program for school and I'm adding a "current price" label. So far so good. I'm trying to make the price display with 2 decimals seeing as without the format it will display prices with 10+ decimals. This is my code:

double aantalProducten [] = {1, 1, 1, 1, 1, 1};

double producten [] = {9.50, 2.95, 1.95, 2.50, 1.00, 1.00};

double totaal [] = {0, 0, 0, 0, 0, 0};

DecimalFormat df = new DecimalFormat("€0.00");

private void BtnPizzaActionPerformed(java.awt.event.ActionEvent 
evt) {                                         
    producten [0] = 9.50;
    aantalProducten[0]++; 
    totaal[0] =+ (producten[0]*aantalProducten[0]);
    LblCurrentPrice.setText(df.format(""+ 
  (totaal[0]+totaal[1]+totaal[2]+totaal[3]+totaal[4]+totaal[5])));

And I've done that for 5 more buttons. However when pressing a button it will tell me: "Cannot format given Object as a Number".

I tried "Arrays.toString" but it gave the same error. When displaying the "current price" without the df.format it will show no error. Any tips?

Answer 1

You can't use DecimalFormat to format a string. You can use it to format double s though:

df.format(totaal[0]+totaal[1]+totaal[2]+totaal[3]+totaal[4]+totaal[5])

You were casting the value of the sum of totals to String by adding "" + to it. Again, there's no DecimalFormat.format(String) method.

Edit:

Maybe you wanted to display each total separately with a space between each one, not the sum, even though that's what you had. This is how you could do that:

df.format(totaal[0])
+ " " + df.format(totaal[1])
+ " " + df.format(totaal[2])
+ " " + df.format(totaal[3])
+ " " + df.format(totaal[4])
+ " " + df.format(totaal[5])