BigDecimal setScale方法语法不起作用

Question

这段代码在我提到的setScale()行中给出了一个错误; 它给我一个错误说Rounding必要.我正在尝试创建一个应用程序,它将接受cp和sp,然后根据利润/损失找到盈利/亏损百分比.有人可以帮我解决BigDecimal声明吗？

```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)

Answer 1

在setScale方法的javadoc中清楚地提到了它

@throws ArithmeticException如果{@code roundingMode == ROUND_UNNECESSARY}并且指定的缩放操作需要舍入.

示例:这将抛出上述异常

new BigDecimal("1200.1234").setScale(2, BigDecimal.ROUND_UNNECESSARY)

因为当你将它的比例缩小到2时,你需要指定如何舍入它 - 向上舍入(1200.13)或向下舍入(1200.12)

如果您只需要两个小数位,请选择舍入模式(以您可接受的为准)