Question

我正在编写文件阅读器，其目的是让用户输入一个代表文本文件中行号的数字。保存此数字的变量的类型为int。但是，当用户输入String时，Java会抛出InputMismatchException异常，而我想要的是在catch子句中有一个循环，我将循环到用户输入有效值，即int。骨架看起来像这样：

 public void _____ throws IOException {
    try {
    // Prompting user for line number
    // Getting number from keyboard
    // Do something with number
    } catch (InputMismatchException e) {
       // I want to loop until the user enters a valid input
       // When the above step is achieved, I am invoking another method here
    }  
}

我的问题是，有哪些可能的技术可以进行验证？谢谢。

Answer 1

while(true){ 
   try { 
        // Prompting user for line number 
        // Getting number from keyboard 
        // Do something with number 
        //break; 
       } catch (InputMismatchException e) { 
            // I want to loop until the user enters a valid input 
            // When the above step is achieved, I am invoking another method here 
       } 
   }

Answer 2

避免使用流量控制的例外。捕获异常，但只打印消息。另外，在循环中需要循环。

这很简单：

public void _____ throws IOException {
    int number = -1;
    while (number == -1) {
        try {
            // Prompt user for line number
            // Getting number from keyboard, which could throw an exception
            number = <get from input>;
        } catch (InputMismatchException e) {
             System.out.println("That is not a number!");
        }  
    }
    // Do something with number
}

Answer 3

您可以避开Exception

Scanner sc = new Scanner(System.in);
while(sc.hasNextLine())
    String input = sc.nextLine();
    if (isNumeric(input) {
        // do something
        // with the number
        break; // break the loop
    }
}

方法isNumeric：

public static boolean isNumeric(String str) {
    return str.matches("^[0-9]+$");
}

如果要使用输入编号的对话框：

String input = JOptionPane.showInputDialog("Input a number:"); // show input dialog

Java - 在try-catch块中循环

3 个答案: