Question

用户将需要输入一个数字来读取电表，如果用户输入的不是数字，则尝试捕获块将初始化，如果用户输入的是负数，则会弹出错误消息，请执行以下操作：虽然很简单，但是我对如何实现for循环感到困惑

    public static int readStartReading(){ 
    int reading = 0;
    Scanner keyboard = new Scanner(System.in);
    boolean problemFlag = false;
    do {
        problemFlag = false;
        try {
            System.out.print("Enter the meter reading at the beginning of the year: ");
            String input = keyboard.nextLine();
            reading = Integer.parseInt(input);// 7. Assign a value to reading through the input device
        } catch (NumberFormatException x){
            problemFlag = true;
            System.out.println("You have to enter a number.");
        } if (reading < 0){
            System.out.println("The beginning meter reading cannot be negative."); }
    } while (reading < 0 || problemFlag);
    return reading;
}

我注意到我的错误。谢谢您的答复

Answer 1

那

public static int readStartReading()
{ 
int reading = -1; 
Scanner keyboard; //remove first reading here

while(1)
{
    try 
    {
        System.out.print("Enter the meter reading at the beginning of the year: ");
        String input = keyboard.nextLine();
        reading = Integer.parseInt(input);// 7. Assign a value to reading through the input device

        //if control reaches here, you have a valid integer, test it
        if (reading >= 0)
            break;
        else
            System.out.println("The beginning meter reading cannot be negative.");
    } 
    catch (NumberFormatException x)
        System.out.println("You have to enter a number.");
} 
return reading;

}

Answer 2

您可以非常简单地将其转换为for循环，但不会有任何区别。在您的情况下，do-while更适合。

public static int readStartReading(){ 
int reading = 0;
Scanner keyboard = new Scanner(System.in);
boolean problemFlag = false;
for(;reading < 0 || problemFlag;)
{
    problemFlag = false;
    try {
        System.out.print("Enter the meter reading at the beginning of the year: ");
        String input = keyboard.nextLine();
        reading = Integer.parseInt(input);// 7. Assign a value to reading through the input device
    } catch (NumberFormatException x){
        problemFlag = true;
        System.out.println("You have to enter a number.");
    } if (reading < 0){
        System.out.println("The beginning meter reading cannot be negative."); }
}
return reading;
}

还有几个小问题

您不需要问题标记
您正在执行两次初始读取，（用户必须输入两次值）

我会这样重写它：

public static int readStartReading()
{ 
int reading = 0;
Scanner keyboard; //remove first reading here

do
{
    try {
        System.out.print("Enter the meter reading at the beginning of the year: ");
        String input = keyboard.nextLine();
        reading = Integer.parseInt(input);// 7. Assign a value to reading through the input device

        //if control reaches here, you have a valid integer, test it
        if (reading < 0)
            System.out.println("The beginning meter reading cannot be negative.");

    } catch (NumberFormatException x){
        reading = -1; //set reading to a negative invalid value
        System.out.println("You have to enter a number.");
    }
} while(reading < 0)
return reading;
}

我如何将其转换为for循环？

2 个答案: