我想为错误的用户输入添加一个 try/catch 块

Question

下面是我的代码，我想在 do/while 循环中添加一个 try/catch 块，以便为除数字以外的用户输入引发异常（即，如果用户输入 20 而不是 20）。我不确定如何编写比较来引发异常。

import java.util.Scanner;

public class Paint1 {

    public static void main(String[] args) {
        Scanner scnr = new Scanner(System.in);
        double wallHeight = 0.0;
        double wallWidth = 0.0;
        double wallArea = 0.0;
        double gallonsPaintNeeded = 0.0;

        double squareFeetPerGallons = 350.0;

        // Prompt user to input wall's height
        System.out.println("Enter wall height (feet): ");
        wallHeight = scnr.nextDouble();
        while (wallHeight <= 0) {
            do {
                System.out.println("Wall height must be a number greater then zero and in arabic numeral format.");
                System.out.println("Enter wall height (feet): ");
                wallHeight = scnr.nextDouble();
            } while (wallHeight <= 0);
        }

        // Prompt user to input wall's width
        System.out.println("Enter wall width (feet): ");
        wallWidth = scnr.nextDouble();
        while (wallWidth <= 0) {
            do {
                System.out.println("Wall width must be a number greater then zero and in arabic numeral format.");
                System.out.println("Enter wall width (feet): ");
                wallWidth = scnr.nextDouble();
            } while (wallWidth <= 0);
        }

        // Calculate and output wall area
        wallArea = (wallHeight * wallWidth);
        System.out.println("Wall area: " + wallArea + " square feet");

        // Calculate and output the amount of paint (in gallons) needed to paint the wall
        gallonsPaintNeeded = (wallArea / squareFeetPerGallons);
        System.out.println("Paint needed: " + gallonsPaintNeeded + " gallons");
    }
}

Answer 1

初始化变量，这样如果 catch 块被执行，它将继续询问数字并在 catch 块中显示错误消息：

wallHeight = 0;
do {
    try {
        // Prompt user to input wall's height
        System.out.println("Enter wall height (feet): ");
        String input = scnr.next();
        wallHeight = Double.parseDouble(input);
    } catch (Exception e) {
        System.out.println("Wall height must be a number greater then zero and in arabic numeral format.");
    }
} while (wallHeight <= 0);

wallWidth = 0;
do {
    try{
        // Prompt user to input wall's width
        System.out.println("Enter wall width (feet): ");
        String input = scnr.next();
        wallWidth = Double.parseDouble(input);
    } catch (Exception e) {
        System.out.println("Wall width must be a number greater then zero and in arabic numeral format.");
    }
} while (wallWidth <= 0);

我要做的另一件事是，由于输入数据可能与双精度数据不同，因此您可以将其读取为字符串，以便消耗它，然后对其进行解析并捕获此异常，否则错误的输入仍然存在并且会导致infinite loop。

另一种可能性是使用scnr.nextLine() 来使用catch 块中的输入，例如：

try {
    // Prompt user to input wall's height
    System.out.println("Enter wall height (feet): ");
    wallHeight = scnr.nextDouble();
} catch (Exception e) {
    System.out.println("Wall height must be a number greater then zero and in arabic numeral format.");
    scnr.nextLine();
}

请注意，您可以摆脱另一个 while，您只需要一个，在这种情况下，我使用了 do/while。