这段代码在我提到setScale（）的那一行上给了我一个错误；
出现“需要舍入”的错误提示。我正在尝试制作一个将使用cp和sp的应用程序，然后根据利润/亏损找到利润/亏损百分比。有人可以用BigDecimal语句帮助我吗？
```java
import java.math.BigDecimal;
import java.math.RoundingMode;
import java.util.Scanner;
abstract class functions
{
abstract void cpSP();
}
public class Percentage
{
static Scanner sc = new Scanner(System.in);
public void cpSP()
{
System.out.println("Enter the Cost Price:");
double CP = sc.nextDouble();
System.out.println("Enter the Selling Price:");
double SP = sc.nextDouble();
if (CP > SP)
{
System.out.println("As the Cost Price is greater than the Selling Price, there will be LOSS.");
System.out.println("Loss = CP - SP");
double loss = CP - SP;
System.out.println("Loss = " + loss);
System.out.println("Now,");
System.out.println("Loss percentage = Loss/CP x 100");
System.out.println("");
double lossPercentage = (loss/CP)*100;
String lPString = Double.toString(lossPercentage);
BigDecimal bd = new BigDecimal(lPString);
bd.setScale(2);
System.out.println("Loss percentage = " + bd + "%" );
}
else if (SP > CP)
{
System.out.println("As the Cost Price is less than the Selling Price, there will be PROFIT.");
System.out.println("Profit = SP - CP");
double profit = SP - CP;
System.out.println("Profit = " + profit);
System.out.println("Now,");
System.out.println("Profit percentage = Profit/CP x 100");
double profitPercentage = (profit / CP)*100;
String pPString = Double.toString(profitPercentage);
BigDecimal bd = new BigDecimal(pPString).setScale(2, RoundingMode.UNNECESSARY);
System.out.println("Proft percentage = " + bd + "%" );
}
else
{
System.out.println("No profit, no loss.");
}
}
public static void main(String[] args)
{
Percentage p = new Percentage();
System.out.println("Select an option:");
System.out.println("1. Find profit/loss percentage where the CP and SP is given.");
int select = sc.nextInt();
if (select == 1)
{
p.cpSP();
}
}
}
```错误是：
Exception in thread "main" java.lang.ArithmeticException: Rounding necessary
at java.math.BigDecimal.commonNeedIncrement(BigDecimal.java:4148)
at java.math.BigDecimal.needIncrement(BigDecimal.java:4204)
at java.math.BigDecimal.divideAndRound(BigDecimal.java:4112)
at java.math.BigDecimal.setScale(BigDecimal.java:2452)
at java.math.BigDecimal.setScale(BigDecimal.java:2386)
at maths.Percentage.cpSP(Percentage.java:45)
at maths.Percentage.main(Percentage.java:64)
最佳答案
在setScale方法的javadoc中明确提到
如果{@code roundingMode == ROUND_UNNECESSARY}和指定的缩放操作需要四舍五入，则@throws ArithmeticException。
例：
这将引发上述异常
new BigDecimal("1200.1234").setScale(2, BigDecimal.ROUND_UNNECESSARY)
因为当您将其比例缩小为2时，您需要指定如何舍入-向上舍入（1200.13）或向下舍入（1200.12）
如果仅需要两位小数，请选择一种舍入模式（您可以接受的任何一种）