英文:
How to catch an Error in a Switch statement when the user entered number doesn't exist
问题
我试图使我的程序防错，该程序基本上是一个迷你计算器。但我不知道如何编写一个“Catch”语句，以便在用户输入不存在的情况下（在我的情况下为任何负数或大于4的数字）进行检测。
public static void main(String[] args) {
System.out.println("你好用户！你想要使用哪种操作？");
System.out.println("1) + \n2) - \n3) * \n4) /");
Scanner operacijai = new Scanner(System.in);
int operacija = operacijai.nextInt();
int n = 1;
do {
try {
switch (operacija) {
case 1:
addingMethod();
n = 2;
break;
case 2:
subtractingMethod();
n = 2;
break;
case 3:
multiplyingMethod();
n = 2;
break;
case 4:
dividingMethod();
n = 2;
break;
}
} catch (Exception e) {
System.out.print("请输入正确的数字！");
}
} while (n == 1);
operacijai.close();
}
英文:
I'm trying to error proof my program that basically works as a mini calculator. But I have no idea how to write a "Catch" statement that would detect when the user enters a case number that doesn't exist, in my case anything that is negative or > 4
System.out.println("Hello user! Which operation would you like to use?");
System.out.println("1) + \n2) - \n3) * \n4) /");
Scanner operacijai = new Scanner(System.in);
int operacija = operacijai.nextInt();
int n=1;
do {
try {
switch (operacija) {
case 1:
addingMethod();
n=2;
break;
case 2:
subtractingMethod();
n=2;
break;
case 3:
multiplyingMethod();
n=2;
break;
case 4:
dividingMethod();
n=2;
break;
}
}
catch(Exception e) {
System.out.print("Enter a correct number!");
}
} while(n==1);
operacijai.close();
} ```
</details>
# 答案1
**得分**: 2
为什么你要不必要地抛出一个 `Exception`？我建议你在 `switch` 中加入一个带有所需错误消息的 `default` 情况。另外，将输入部分移动到循环内，这样它就会继续获取输入。
我还建议你使用 `nextLine()` 而不是 `nextInt()`。了解更多信息，请查看 https://stackoverflow.com/questions/13102045/scanner-is-skipping-nextline-after-using-next-or-nextfoo。
```java
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
System.out.println("Hello user! Which operation would you like to use?");
System.out.println("1) + \n2) - \n3) * \n4) /");
Scanner operacijai = new Scanner(System.in);
int operacija = 0, n = 1;
boolean valid;
do {
do {
valid = true;
try {
operacija = Integer.parseInt(operacijai.nextLine());
} catch (NumberFormatException e) {
System.out.println("Enter an integer only.");
valid = false;
}
} while (!valid);
switch (operacija) {
case 1:
System.out.println("addingMethod()");
n = 2;
break;
case 2:
System.out.println("subtractingMethod()");
n = 2;
break;
case 3:
System.out.println("multiplyingMethod()");
n = 2;
break;
case 4:
System.out.println("dividingMethod()");
n = 2;
break;
default:
System.out.println("Invalid input");
}
} while (n == 1);
}
}
一个示例运行:
Hello user! Which operation would you like to use?
1) +
2) -
3) *
4) /
5
Invalid input
另一个示例运行:
Hello user! Which operation would you like to use?
1) +
2) -
3) *
4) /
a
Enter an integer only.
5
Invalid input
2
subtractingMethod()
英文:
Why do you want to throw an Exception unnecessarily? I suggest you just put a default case in your switch with the required error message. Also, move the input part inside the loop, so that it continues to take input.
I also suggest you use nextLine() instead of nextInt(). Check https://stackoverflow.com/questions/13102045/scanner-is-skipping-nextline-after-using-next-or-nextfoo to learn more about it.
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
System.out.println("Hello user! Which operation would you like to use?");
System.out.println("1) + \n2) - \n3) * \n4) /");
Scanner operacijai = new Scanner(System.in);
int operacija = 0, n = 1;
boolean valid;
do {
do {
valid = true;
try {
operacija = Integer.parseInt(operacijai.nextLine());
} catch (NumberFormatException e) {
System.out.println("Enter an integer only.");
valid = false;
}
} while (!valid);
switch (operacija) {
case 1:
System.out.println("addingMethod()");
n = 2;
break;
case 2:
System.out.println("subtractingMethod()");
n = 2;
break;
case 3:
System.out.println("multiplyingMethod()");
n = 2;
break;
case 4:
System.out.println("dividingMethod()");
n = 2;
break;
default:
System.out.println("Invalid input");
}
} while (n == 1);
}
}
A sample run:
Hello user! Which operation would you like to use?
1) +
2) -
3) *
4) /
5
Invalid input
Another sample run:
Hello user! Which operation would you like to use?
1) +
2) -
3) *
4) /
a
Enter an integer only.
5
Invalid input
2
subtractingMethod()
答案2
得分: 0
你还可以处理在default中的使用情况。完全取决于您的用例，您可以如下处理异常，还可以创建自定义异常并从default中抛出，类似于：
System.out.println("Hello user! Which operation would you like to use?");
System.out.println("1) 加法\n2) 减法\n3) 乘法\n4) 除法");
Scanner operacijai = new Scanner(System.in);
int operacija = operacijai.nextInt();
int n=1;
do {
try {
switch (operacija) {
case 1:
addingMethod();
n=2;
break;
case 2:
subtractingMethod();
n=2;
break;
case 3:
multiplyingMethod();
n=2;
break;
case 4:
dividingMethod();
n=2;
break;
default:
System.out.print("输入正确的数字！");
throw new CustomException();
}
}
catch(CustomException e) {
System.out.print("输入正确的数字！");
}
} while(n==1);
operacijai.close();
注意：这里的代码只是翻译了您提供的部分内容，并没有对代码逻辑进行任何更改。
英文:
You can also handle the use case in default
It is totally upto your use-case how you are handling the exception, you can also create your custom exception and throw from default
something like:
System.out.println("Hello user! Which operation would you like to use?");
System.out.println("1) + \n2) - \n3) * \n4) /");
Scanner operacijai = new Scanner(System.in);
int operacija = operacijai.nextInt();
int n=1;
do {
try {
switch (operacija) {
case 1:
addingMethod();
n=2;
break;
case 2:
subtractingMethod();
n=2;
break;
case 3:
multiplyingMethod();
n=2;
break;
case 4:
dividingMethod();
n=2;
break;
default:
System.out.print("Enter a correct number!")
throw new CustomException();
}
}
catch(CustomException e) {
System.out.print("Enter a correct number!");
}
} while(n==1);
operacijai.close();
}
答案3
得分: 0
已找到一种使用默认情况的清晰方法。
public static void main(String[] args) {
System.out.println("你好！请选择要使用的操作：");
System.out.println("1) 加法\n2) 减法\n3) 乘法\n4) 除法");
Scanner operacijai = new Scanner(System.in);
int operacija;
do {
operacija = operacijai.nextInt();
switch (operacija) {
case 1:
addingMethod();
break;
case 2:
subtractingMethod();
break;
case 3:
multiplyingMethod();
break;
case 4:
dividingMethod();
break;
default:
System.out.print("请输入正确的数字！");
}
} while (operacija < 1 || operacija > 4);
operacijai.close();
}
英文:
Figured out a clean way of doing this with default case.
System.out.println("Hello user! Which operation would you like to use?");
System.out.println("1) + \n2) - \n3) * \n4) /");
Scanner operacijai = new Scanner(System.in);
int operacija;
do {
operacija = operacijai.nextInt();
switch (operacija) {
case 1:
addingMethod();
break;
case 2:
subtractingMethod();
break;
case 3:
multiplyingMethod();
break;
case 4:
dividingMethod();
break;
default:
System.out.print("Enter a correct number!");
}
} while(operacija < 1 || operacija > 4);
operacijai.close();
}
</details>
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