How to calculate monetary values in Java

There are many monetary values calculation in the financial or e-commerce application, and there is one question that arises for this – Should we use double or float data type to represent the monetary values?

Answer: Always uses java.math.BigDecimal to represent the monetary values.

1. Double or Float?

Here is an example of using double and float to represent the monetary values in Java.

package com.mkyong;

import java.text.DecimalFormat;

public class JavaMoney {

    private static DecimalFormat df = new DecimalFormat("0.00");

    public static void main(String[] args) {

        System.out.println(2.00 - 1.1);
        System.out.println(2.00 - 1.2);
        System.out.println(2.00 - 1.3);
        System.out.println(2.00 - 1.4);
        System.out.println(2.00 - 1.5);
        System.out.println(2.00 - 1.6);
        System.out.println(2.00 - 1.7);
        System.out.println(2.00 - 1.8);
        System.out.println(2.00 - 1.9);
        System.out.println(2.00 - 2);

        System.out.println("--------------------");

        double i = 2.0;
        double j = 1.7;

        System.out.println("double : " + (i - j));
        System.out.println("double : " + df.format(i - j));

        float i2 = 2.0f;
        float j2 = 1.7f;

        System.out.println("float : " + (i2 - j2));
        System.out.println("float : " + df.format(i2 - j2));

    }

}

Output – It cannot calculate all the decimals precisely.

0.8999999999999999
0.8
0.7
0.6000000000000001
0.5
0.3999999999999999
0.30000000000000004
0.19999999999999996
0.10000000000000009
0.0
--------------------
double : 0.30000000000000004
double : 0.30
float : 0.29999995
float : 0.30

2. BigDecimal

To avoid the decimal issue above, we can use BigDecimal to represent the monetary values; furthermore, we can control the BigDecimal scale much more straightforward.

package com.mkyong;

import java.math.BigDecimal;
import java.math.RoundingMode;

public class JavaMoney2 {

    public static void main(String[] args) {

        System.out.println("--- BigDecimal-----");
        System.out.println(BigDecimal.valueOf(2.00).subtract(BigDecimal.valueOf(1.1)));
        System.out.println(BigDecimal.valueOf(2.00).subtract(BigDecimal.valueOf(1.2)));
        System.out.println(BigDecimal.valueOf(2.00).subtract(BigDecimal.valueOf(1.3)));
        System.out.println(BigDecimal.valueOf(2.00).subtract(BigDecimal.valueOf(1.4)));
        System.out.println(BigDecimal.valueOf(2.00).subtract(BigDecimal.valueOf(1.5)));
        System.out.println(BigDecimal.valueOf(2.00).subtract(BigDecimal.valueOf(1.6)));
        System.out.println(BigDecimal.valueOf(2.00).subtract(BigDecimal.valueOf(1.7)));
        System.out.println(BigDecimal.valueOf(2.00).subtract(BigDecimal.valueOf(1.8)));
        System.out.println(BigDecimal.valueOf(2.00).subtract(BigDecimal.valueOf(1.9)));
        System.out.println(BigDecimal.valueOf(2.00).subtract(BigDecimal.valueOf(2)));

        System.out.println("--------------------");

        BigDecimal i = BigDecimal.valueOf(2.0);
        BigDecimal j = BigDecimal.valueOf(1.7);

        System.out.println("double : " + i.subtract(j));
        System.out.println("double : " + i.subtract(j).setScale(5, RoundingMode.HALF_UP));

    }

}

Output – BigDecimal performs exact decimal arithmetic.

--- BigDecimal-----
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
--------------------
double : 0.3
double : 0.30000

References

• BigDecimal JavaDoc
• How to Use Java BigDecimal: A Tutorial
• Java 8 – How to Sum BigDecimal using Stream?