Java：Do-While 循环中的 Try-Catch 语句
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/22004921/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Java: Try-Catch statement within a Do-While loop
提问by
I am trying to execute a bit of code that scans for a user input value. This action is contained in a custom method I wrote, named getTriangleDim(); the method reads in the users int value, makes sure it is within a certain range, and then returns the int value that was entered. The method works great and I have no issues with it.
我正在尝试执行一些扫描用户输入值的代码。此操作包含在我编写的自定义方法中，名为 getTriangleDim(); 该方法读取用户的 int 值，确保它在一定范围内，然后返回输入的 int 值。该方法效果很好，我对此没有任何问题。
The problem arises when I enter a non-int value for my getTriangleDim() method. It gives me an InputMismatchException error. I have written a try-catch statement into a do-while loop to attempt to fix this issue. But this is the first time I have ever used a try-catch statement, and I am apparently missing something.
当我为 getTriangleDim() 方法输入一个非整数值时，问题就出现了。它给了我一个 InputMismatchException 错误。我已将 try-catch 语句写入 do-while 循环以尝试解决此问题。但这是我第一次使用 try-catch 语句，显然我遗漏了一些东西。
Here is the code for the try-catch statement nested within the do-while loop:
下面是嵌套在 do-while 循环中的 try-catch 语句的代码：
//loop to scan for triangle dimension
boolean bError = true;
int triangle;
do{
try {
triangle = getTriangleDim();
bError=false;
}
catch (Exception e){
System.out.println("You did not enter an integer, please enter an integer value");
triangle = getTriangleDim();
}
}while (bError);
if i test it by entering a char value in place of the int, it actually catches the error once, and then prints my "you did not....." statement. But if I re-enter another non-int number, I get a runtime error again that says.......you guessed it........ InputMismatchException error.
如果我通过输入一个字符值代替 int 来测试它，它实际上会捕获一次错误，然后打印我的“你没有......”语句。但是如果我重新输入另一个非整数数字，我会再次收到一个运行时错误，说......你猜对了...... InputMismatchException 错误。
The code for my method is here:
我的方法的代码在这里：
//method for scanning triangle dimensions from keyboard
public static int getTriangleDim(){
int triangle = 0;
Scanner keyboard = new Scanner(System.in);
do{
System.out.print("Enter a non-zero integer length (+/-1 - +/-16): ");
triangle = keyboard.nextInt();
if((!(triangle <= 16 && triangle >= 1))&&(!(triangle >= -16 && triangle <= -1)))
System.out.println("Inpute value outside of range");
}while((!(triangle <= 16 && triangle >= 1))&&(!(triangle >= -16 && triangle <= -1)));
return triangle;
}
I need the Do-While loop to continue, but I keep getting these errors.
我需要 Do-While 循环才能继续，但我不断收到这些错误。
采纳答案by Henry Keiter
There's no need to ask for input in the catchblock. You're already in a loop, so you can catch the exception, tell the user to give you valid input, and then you don't have to do anything else--you'll loop back around to the beginning.
无需在catch块中要求输入。你已经在一个循环中，所以你可以捕捉异常，告诉用户给你有效的输入，然后你不必做任何其他事情——你将循环回到开头。
do{
try {
triangle = getTriangleDim();
bError=false;
} catch (Exception e){
System.out.println("You did not enter an integer, please enter an integer value");
// Don't do anything else in here: we will loop back to the beginning again and get new input!
}
}while (bError);
As a side note (and as you've noticed), your code won't currently compile if you try to use triangleoutside of that tryblock, because "triangle might not have been initialized". This is due to the fact that the compiler cannot determine at compile-time what your program will do at run-time: that is, the compiler cannot see that trianglewill always be initialized within that loop. So your variable declaration ought to also set triangleto some default value. 0is the normal default for int, but use whatever makes sense in your program (it looks like 0is fine, based on your getTriangleDimcode).
作为旁注（正如您已经注意到的），如果您尝试triangle在该try块之外使用，您的代码当前不会编译，因为"triangle might not have been initialized". 这是因为编译器无法在编译时确定您的程序将在运行时做什么：也就是说，编译器看不到它triangle总是在该循环内初始化。所以你的变量声明也应该设置triangle为一些默认值。0是 的正常默认值int，但请使用您程序中有意义的任何内容（0根据您的getTriangleDim代码，它看起来很好）。
int triangle = 0;
do { // etc.
This way you can "promise" the compiler that trianglewill have a value by the time you leave the loop, and you'll be able to use it elsewhere.
通过这种方式，您可以“承诺”在triangle您离开循环时将具有值的编译器，并且您将能够在其他地方使用它。
