大数字的计算

package object;

import java.math.BigDecimal;
import java.math.BigInteger;

/**
 * @author dayu
 * @Describe 大数字的计算
 */
public class BigIntegerDemo {
    public static void main(String[] args) {
        BigInteger bigInteger1 = new BigInteger("45645645645645645645645645645645645612321321312321312321456");
        BigInteger bigInteger2 = new BigInteger("45645645645612321321312321312321");
        System.out.println("加法：" + bigInteger1.add(bigInteger2));
        System.out.println("减法：" + bigInteger1.subtract(bigInteger2));
        System.out.println("乘法：" + bigInteger1.multiply(bigInteger2));
        System.out.println("除法：" + bigInteger1.divide(bigInteger2));
        BigInteger[] divideAndRemainder = bigInteger1.divideAndRemainder(bigInteger2);
        System.out.println("商商：" + divideAndRemainder[0] + ",余" + divideAndRemainder[1]);

        System.out.println(roundAndHalf(1234556.1415354,2));
    }

    /**
     * ·四舍五入的进位方法
     * @param num 源数据
     * @param scale 进位数
     * @return
     */
    private static double roundAndHalf(double num,int scale) {
         return new BigDecimal(num).divide(new BigDecimal(1), scale, BigDecimal.ROUND_HALF_UP).doubleValue();
    }

}

一般计算：

package object;

/**
 * @author dayu
 */
public class MathDemo {
    public static void main(String[] args) {

        long round = Math.round(12.3);
        System.out.println(round);
        //自定义方法
        double round3 = round(123.563482, 4);
        System.out.println(round3);
    }

    /**
     * ·保留小数的四舍五入
     * @param num 原始数据源
     * @param scale 要保留的小数
     * @return
     */
    public static double round(double num, int scale) {
        return Math.round(num * Math.pow(10, scale)) / Math.pow(10, scale);
    }
}

原文地址：https://www.cnblogs.com/dayu007/p/10471657.html