详解
import java.math.BigDecimal;
import java.math.BigInteger;
import java.util.Scanner;
public class Main {
	public static Scanner cin = new Scanner(System.in);
	public static void main(String[] args) {
		BigDecimal a = new BigDecimal("4.51");
		BigDecimal b = new BigDecimal("1.5");
		System.out.println("a + b =" + a.add(b));
		System.out.println("a - b =" + a.subtract(b));
		System.out.println("a * b =" + a.multiply(b));
		//下面的不能整除,会报错,可以指定保留小数即可
//		System.out.println("a / b =" + a.divide(b));
		//第二个参数表示小数点后保留位数
		System.out.println("a / b =" + a.divide(b,1));
		System.out.println("a / b =" + a.divide(b,2));
	}
}