How to Correctly Round Doubles to Two Decimal Places in Java?

Rounding to Two Decimal Places in Java

Many developers encounter challenges when attempting to round floating-point numbers to specific decimal places in Java. This is particularly true when the desired output must remain a double.

One common approach involves utilizing Math.round(), as demonstrated in the following code:

class Round {
    public static void main(String[] args) {

        double a = 123.13698;
        double roundOff = Math.round(a * 100) / 100;
        
        System.out.println(roundOff);
    }
}

However, this approach often fails to produce the desired result. Instead of rounding to 123.14, it outputs 123.

To rectify this issue, a slight modification to line 4 is required:

double roundOff = Math.round(a * 100.0) / 100.0;

By adding .0 to the multiplication factor, the result is cast to a double with two decimal places. This ensures that the final result also has two decimal places.

Alternatively, as suggested by @Rufein, one can cast the rounded value to a double:

double roundOff = (double) Math.round(a * 100) / 100;

This approach also effectively produces the desired output of 123.14 with two decimal places.

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