JavaJDK-从double到int的可能有损转换

因此，我最近编写了以下代码：

    import java.util.Scanner;

public class TrainTicket
{
      public static void main (String args[])
      {

         Scanner money = new Scanner(System.in);
         System.out.print("Please type in the type of ticket you would like to buy.\nA. Child B. Adult C. Elder.");
         String type = money.next();
         System.out.print("Now please type in the amount of tickets you would like to buy.");
         int much = money.nextInt();
         int price = 0;
         switch (type)
          {
            case "A":
            price = 10;
            break;
            case "B":
            price = 60;
            break;
            case "C":
            price = 35;
            break;
            default:
            price = 0;
            System.out.print("Not a option ;-;");
           }
          if (price!=0)
          {
            int total2 = price* much* 0.7;
            System.out.print("Do you have a coupon code? Enter Y or N");
            String YN = money.next();
            if (YN.equals("Y"))
            {
             System.out.print("Please enter your coupon code.");
             int coupon = money.nextInt();
             if(coupon==21)
             {
              System.out.println("Your total price is " + "$" + total2 + ".");
             }
             else
             {
              System.out.println("Invalid coupon code, your total price is " + "$" + price* much + ".");
             }
            }
            else
            {
            System.out.println("Your total price is " + "$" + price* much + "." ); 
            }
          }

       money.close();
      }
}

int total2= (int) price*much*0.7;
 /*(int) tells compiler that you are aware      of what you are doing.*/
 //also called as type casting

但是，它始终显示以下内容：

TrainTicket.java:31: error: incompatible types: possible lossy conversion from double to int
            int total2 = price* much* 0.7;

当我尝试使用cmd运行它时

有人能帮我解释一下我犯的错误吗？感谢您的帮助：）。

---

谢谢

您试图将

price*much*0.7

赋值给整数变量，这是一个浮点值（一个

double

）。

double

不是精确整数，因此通常

int

变量不能包含

double

值

例如，假设计算结果为

12.6

。您不能将

12.6

保存在整数变量中，但可以舍弃分数，只存储

12

如果您不担心丢失的分数，请将您的数字转换为

int

，如下所示：

int total2 = (int) (price* much* 0.7);

或者可以将其四舍五入到最接近的整数

int total2 = (int) Math.round(price*much*0.7);

---

将

double

转换为

int

时，值的精度将丢失。 例如 将4.8657（双精度）转换为int时，int值将为4。Primitive

int

不存储十进制数。因此，将丢失0.8657

在您的例子中，0.7是一个双精度值（除非提到float-0.7f，否则默认情况下浮点被视为double）。 当您计算

price*much*0.7

时，答案是一个双精度值，因此编译器不允许您将其存储在类型整数中，因为可能会丢失精度。这就是

可能的有损转换

，您可能会丢失精度

那么你能做些什么呢？ 你需要告诉编译器你真的想这么做，你需要告诉它你知道你在做什么。 因此，使用以下代码显式地将double转换为int：

    import java.util.Scanner;

public class TrainTicket
{
      public static void main (String args[])
      {

         Scanner money = new Scanner(System.in);
         System.out.print("Please type in the type of ticket you would like to buy.\nA. Child B. Adult C. Elder.");
         String type = money.next();
         System.out.print("Now please type in the amount of tickets you would like to buy.");
         int much = money.nextInt();
         int price = 0;
         switch (type)
          {
            case "A":
            price = 10;
            break;
            case "B":
            price = 60;
            break;
            case "C":
            price = 35;
            break;
            default:
            price = 0;
            System.out.print("Not a option ;-;");
           }
          if (price!=0)
          {
            int total2 = price* much* 0.7;
            System.out.print("Do you have a coupon code? Enter Y or N");
            String YN = money.next();
            if (YN.equals("Y"))
            {
             System.out.print("Please enter your coupon code.");
             int coupon = money.nextInt();
             if(coupon==21)
             {
              System.out.println("Your total price is " + "$" + total2 + ".");
             }
             else
             {
              System.out.println("Invalid coupon code, your total price is " + "$" + price* much + ".");
             }
            }
            else
            {
            System.out.println("Your total price is " + "$" + price* much + "." ); 
            }
          }

       money.close();
      }
}

int total2= (int) price*much*0.7;
 /*(int) tells compiler that you are aware      of what you are doing.*/
 //also called as type casting

在您的情况下，由于您正在计算成本，我建议您将变量

total2

声明为double或float类型

double total2=price*much*0.7;
 float total2=price*much*0.7;
 //will work

---

@billc.cn的金额通常用小数表示，这就是我建议它的原因！我的意思是说用双打代替浮球。。。。浮点数的精度损失太快，即使在每天的情况下也无法使用。