Question

我试图找出为什么在输出小数时%.2f声明在我的代码中不起作用，我检查了其他类似的问题，但我似乎无法在特定问题中找到问题我收到的逻辑错误。当我编译我的程序它编译得很好，我去运行它，一切都输出正常，直到我得到最终的成本，我试图只显示小数点后2位的十进制值。

我在主题“main”

中遇到异常

Java.util.illegalformatconversionexception  f! = Java.lang.string
At java.util.Formatter$formatspecifier.failconversion(Unknown Source)
At java.util.Formatter$formatspecifier.printFloat(Unknown Source)
At java.util.Formatter.format(Unknown Source)
At java.io.printstream.format(Unknown Source)
At java.io.printstream.printf(Unknown Source)
At Cars.main(Cars.java:27)

这是我的代码：

import java.util.Scanner;
public class Cars
{

  public static void main(String [] args)
  {
    Scanner input = new Scanner(System.in);

    int carYear, currentYear, carAge;

    double costOfCar, salesTaxRate;
    double totalCost;

    String carModel;
    System.out.println("Please enter your favorite car model.");
        carModel = input.nextLine();
    System.out.println("Please enter the  year of the car");
        carYear = input.nextInt();
    System.out.println("Please enter the current year.");
        currentYear = input.nextInt();
        carAge = currentYear - carYear;
    System.out.println("How much does the car cost?");
        costOfCar = input.nextDouble();
    System.out.println("What is the sales tax rate?");
        salesTaxRate = input.nextDouble();
        totalCost = (costOfCar + (costOfCar * salesTaxRate));
    System.out.printf("The model of your favorite car is" + carModel + ", the car is" + " " + carAge + " " + " years old, the total of the car is" + " " + "%.2f",totalCost + " " + " dollars."); 

    }
}

我不确定是什么导致了这个问题。

Answer 1

尝试：

System.out.printf("The model of your favorite car is %s, the car is %d years old, the total of the car is %.2f dollars.", carModel, carAge, totalCost);

或者更具可读性：

System.out.printf("The model of your favorite car is %s," +
                  " the car is %d years old," +
                  " the total of the car is %.2f dollars.",
                  carModel, carAge, totalCost);

Answer 2

这是因为%.2f被该方法调用中的整个第二个参数替换。问题是通过在f中指定%.2f，您说第二个参数是float或double。在这种情况下，第二个参数是totalCost + " " + " dollars."，它计算为字符串。

要解决此问题，您需要将第二个参数设为float或double。这可以通过将+ " " + " dollars."从第二个参数的末尾移动到第一个参数的结尾来实现，如下所示：

System.out.printf("The model of your favorite car is" + carModel + ", the car is" + " " + carAge + " " + " years old, the total of the car is" + " " + "%.2f" + " " + " dollars.",totalCost);

您还可以从该行中删除许多不必要的连接，从而产生以下结果：

System.out.printf("The model of your favorite car is" + carModel + ", the car is " + carAge + " years old, the total of the car is %.2f dollars.", totalCost);

Answer 3

变量必须作为System.out.printf（）函数的参数。＆＃34;％。2f＆＃34;将被作为第二个参数传递的double值替换。

例如：

    System.out.printf("The value is %.2f", value);

对于其他变量类型和多个变量也是如此，

    String str = "The value is: ";
    double value = .568;
    System.out.printf("%s %.2f", str, value);

这将输出：＆＃34;值为：.57＆＃34;

在java中显示2位的输出小数

3 个答案: