JavaSE BigDecimal

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

public class BigDecimalTest {
    public static void main(String[] args) {
        BigDecimal s1 = new BigDecimal(10);
        BigDecimal s2 = new BigDecimal(3);
        //加
        BigDecimal s3 = s1.add(s2);
        System.out.println(s3);
        //减
        BigDecimal s4 = s1.subtract(s2);
        System.out.println(s4);
        //乘
        BigDecimal s5 = s1.multiply(s2);
        System.out.println(s5);
        //除
        BigDecimal s6 = s1.divide(s2,3,RoundingMode.HALF_DOWN);
        System.out.println(s6);
    }
}