注意假设结果是无限位小数，不指定位数进行四舍五入的话会报错

import java.util.Scanner;
import java.math.BigDecimal;

public class Main {
	public static void main(String args[]){
		Scanner in = new Scanner(System.in);
		BigDecimal a = in.nextBigDecimal();
		BigDecimal b = in.nextBigDecimal();
		
		System.out.println("Add " + a.add(b));
		System.out.println("Sub " + a.subtract(b));
		System.out.println("Mul " + a.multiply(b));
		System.out.println("divide " + a.divide(b));//此处假设结果是无限循环。就会报错
		System.out.println("四舍五入： " + a.divide(b,5,BigDecimal.ROUND_HALF_UP));
		//第二个參数是小数位数  a.divide(b,5,BigDecimal.ROUND_HALF_UP).doubleValue;
		
		double d1 = 3.1415926; 
		BigDecimal t1 = new BigDecimal(d1); //依次能够进行doubleToBigDecimal的转换
		
		int d2 = 3214856;
		BigDecimal t2 = new BigDecimal(d2);
		
		BigDecimal t3 = new BigDecimal("843269136");
		
		System.out.println("dobule TO : " + t1);
		System.out.println("Int to : " + t2);
		System.out.println("String to : " + t3);	
	}
}