Restricting decimal places in an array

Question

Currently, the output of this array has a too large decimal place trail. How can I restrict this to say 2 decimal places? By this I mean the array 'percentage1'. I've seen methods to do it online, but I don't understand how I would implement those methods into the code as shown below.

int[] correct1 = {20, 20, 13, 15, 22, 18, 19, 21, 23, 25};
int[] incorrect1 = {2, 1, 5, 2, 2, 5, 8, 1, 0, 0};

    double[] percentage1 = new double[correct1.length];
    for(int a = 0; a < correct1.length; a++ ){ 
             percentage1[a] = (((double)correct1[a] / (correct1[a] + incorrect1[a]))*100);
        }

Any help would be very much appreciated. Thanks

Answer 1

Please try adding a DecimalFormat object.

1. Add this to the beginning of the loop, it declares the format you're looking for - 2 decimal places: DecimalFormat df = new DecimalFormat("#.##");

2. Format it using format, then convert it back into a double. The reason why you need to restore it back is that format returns a String.

   percentage1[a] = Double.valueOf(df.format((((double)correct1[a] / (correct1[a] + incorrect1[a]))*100)));

See revised code below:

public static void main(String[] args) {
    // TODO Auto-generated method stub
    int[] correct1 = {20, 20, 13, 15, 22, 18, 19, 21, 23, 25};
    int[] incorrect1 = {2, 1, 5, 2, 2, 5, 8, 1, 0, 0};

        double[] percentage1 = new double[correct1.length];
        DecimalFormat df = new DecimalFormat("#.##");
        for(int a = 0; a < correct1.length; a++ ){ 
                 percentage1[a] = Double.valueOf(df.format((((double)correct1[a] / (correct1[a] + incorrect1[a]))*100)));
                 System.out.println(percentage1[a]);
            }

}

Sample result:

90.91
95.24
72.22
88.24
91.67
78.26
70.37
95.45
100.0
100.0

Answer 2

You can't. Doubles don't have decimal places. They have binary places. If you want decimal places you have to use a decimal radix, i.e. a String created by DecimalFormat, or a BigDecimal.

Proof here.