处理输入非整数变量Java的错误

Question

我正在编写一个程序，它接受用户输入的整数和字符串，并对字符串执行操作。我已经创建了这个程序，它运行得很好，我的问题是，我现在正在尝试处理有人为userInput输入非整数值的错误，我不知道该怎么做。我曾尝试使用Try-Catch语句，但在这样做时，我不断收到userInput变量的错误消息

我想做的是当userInput不是整数时，将布尔inputError设置为true，这样我的while循环反复要求用户输入整数，直到他们输入为止

public class Q3 {
public static void main(String[] args)
{   
    Scanner in = new Scanner(System.in);
    boolean inputError = false;

    try{
        System.out.print("Please enter a number between 5 and 10, inclusively: ");
        String userInput1 = in.nextLine();
        int userInput = Integer.parseInt(userInput1);
    }
    catch(InputMismatchException e)
    {
        inputError = true;
    }

    // If userInput is not between 5 and 10, set the boolean inputError to true.
    if (userInput < 5 || userInput > 10)
    {
        inputError = true;
    }

    // Repeatedly ask for user input if they do not enter a number between 5 and 10.
    while(inputError)
    {
        System.out.print("Error. Please enter a number between 5 and 10, inclusively: ");
        userInput = in.nextInt();
        in.nextLine();
        if (userInput >= 5 || userInput <= 10)
        {
            inputError = false;
        }
    }

    // Take user's input for the string.
    System.out.print("Please enter a string of length 6 characters: ");
    String textToChange = in.nextLine();
    int length = 6;
    String printArray = "";
    String wordsOdd = "";
    String finalConcat ="";
    String transitionString="";

    // Print error if text is not 6 characters long.
    while(textToChange.length() != 6) 
    {
        System.out.println("Error! Enter a string of length 6.");
        textToChange = in.nextLine();
    }

Answer 1

您需要检查循环内输入有效性的所有代码：

Scanner in = new Scanner(System.in);
boolean inputError = true;
int userInput = 0;

while (inputError) {
    try {
        System.out.print("Please enter a number between 5 and 10, inclusively: ");
        String userInput1 = in.nextLine();
        userInput = Integer.parseInt(userInput1);
        inputError = (userInput < 5 || userInput > 10);
    } catch (NumberFormatException e) {
        inputError = true;
    }
    if (inputError)
        System.out.println("Wrong input");        
}
System.out.print("Please enter a string of length 6 characters: ");
..................................

在将有效整数作为userInput传递之前，上述循环永远不会结束

Answer 2

问题是变量“userInput”是在try-catch块内声明的，这意味着在该块结束后将不存在。您应该做的是在主方法开始时初始化它们，以便可以从主方法内的任何代码块全局访问它们

int userInput = 1; // Set default initialisation. 
String userInput1 = "";

try {
  NumberFormat.getInstance().parse(userInput1);
  userInput = Integer.parseInt(userInput1);
}
catch(ParseException e) {
  inputError = true; //not a number
}