为什么在我的程序中，验证检查中的三个while循环中有两个被跳过?

Question

为什么我的第一个while循环检查用户输入的有效性，而其他两个月和年的while循环只是被跳过(忽略)?我试图让用户正确输入日期，而不是让他们输入不可能的值。

// A read() method to read in the account details from the user
boolean success = false;
public void read()
{
    Scanner keyboardIn = new Scanner(System.in);        
    System.out.println("ENTER ACCOUNT DETAILS: ");
    System.out.print("User Title: ");
    String title = keyboardIn.nextLine();
    name.setTitle(title);
    System.out.print("User First name: ");
    String firstname = keyboardIn.nextLine();
    name.setFirstName(firstname);
    System.out.print("User Second name: ");
    String secondname = keyboardIn.nextLine();
    name.setSurname(secondname);
    System.out.print("Account Address: ");
    address = keyboardIn.nextLine();
    // To make sure day is entered correctly (1 - 31)
    while(!success)
    {
        try
        {
            System.out.print("Enter the day the account opened: ");
            int d = keyboardIn.nextInt();
            dateOpened.setDay(d);
            success = true;
        }catch(Exception e)
        {
            System.out.println(e.getMessage());
        }
    }
    // To make sure month is entered correctly (1 - 12)  
    while(!success)
    {   
        try
        {
            System.out.print("Enter the month the account opened: ");
            int m = keyboardIn.nextInt();
            dateOpened.setMonth(m);
            success = true;
        }catch(Exception e)
        {
            System.out.println(e.getMessage());
        }
    }
     // To make sure year is entered correctly (< 1900 not permitted)
    while(!success)
    {   
        try
        {
            System.out.print("Enter the year the account opened: ");
            int y = keyboardIn.nextInt();
            dateOpened.setYear(y);
            success = true;
        }catch(Exception e)
        {
            System.out.println(e.getMessage());
        }
    }
    System.out.print("Enter the initial balance: ");
    balance = keyboardIn.nextDouble();
    System.out.print("Enter the overdraft amount: ");
    overdraftAmount = keyboardIn.nextDouble();
    System.out.println("Account number: " + accountNo);
    System.out.println();
}

Answer 1

由于第一个while循环的循环条件仅在success为true时终止，因此其他两个while循环的成功将为true，并且它们将永远不会运行。

我不建议使用"success"作为循环条件。你可以这样写

System.out.print("Enter the day the account opened: ");
int d = keyboardIn.nextInt();
while(d < 1 || d>31){
System.out.print("Enter the day the account opened: ");
d = keyboardIn.nextInt();
}
//set d as day in object

Answer 2

这可能有两个原因，第一个是用户输入的数据不是整数，这会抛出InputMismatchException异常或在dateOpened.setDay(d)失败的行中，如果dateOpened为null或者如果方法setDay失败，则不会将success变量设置为true

Answer 3

在第一次while循环之后，不要重置循环条件"success"。

解决这个问题的一种方法是在每次循环后重置它

另一方面，在较小的方法中实现它，并使条件变量局部化，也可以解决这个问题。

public void read()
{
    Scanner keyboardIn = new Scanner(System.in);        
    System.out.println("ENTER ACCOUNT DETAILS: ");
    System.out.print("User Title: ");
    String title = keyboardIn.nextLine();
    name.setTitle(title);
    System.out.print("User First name: ");
    String firstname = keyboardIn.nextLine();
    name.setFirstName(firstname);
    System.out.print("User Second name: ");
    String secondname = keyboardIn.nextLine();
    name.setSurname(secondname);
    System.out.print("Account Address: ");
    address = keyboardIn.nextLine();
    // To make sure day is entered correctly (1 - 31)
    readDay(keyboardIn);
    // To make sure month is entered correctly (1 - 12)  
    readMonth(keyboardIn);
     // To make sure year is entered correctly (< 1900 not permitted)
    readYear(keyboardIn);
    System.out.print("Enter the initial balance: ");
    balance = keyboardIn.nextDouble();
    System.out.print("Enter the overdraft amount: ");
    overdraftAmount = keyboardIn.nextDouble();
    System.out.println("Account number: " + accountNo);
    System.out.println();
}
private void readDay(Scanner keyboardIn){
    boolean success = false;
    while(!success)
    {
        try
        {
            System.out.print("Enter the day the account opened: ");
            int d = keyboardIn.nextInt();
            dateOpened.setDay(d);
            success = true;
        }catch(Exception e)
        {
            System.out.println(e.getMessage());
            keyboardIn.next();
        }
    }
}
private void readMonth(Scanner keyboardIn){
    boolean success = false;
    while(!success)
    {   
        try
        {
            System.out.print("Enter the month the account opened: ");
            int m = keyboardIn.nextInt();
            dateOpened.setMonth(m);
            success = true;
        }catch(Exception e)
        {
            System.out.println(e.getMessage());
            keyboardIn.next();
        }
    }
}
private void readMonth(Scanner keyboardIn){
    boolean success = false;
    while(!success)
    {   
        try
        {
            System.out.print("Enter the year the account opened: ");
            int y = keyboardIn.nextInt();
            dateOpened.setYear(y);
            success = true;
        }catch(Exception e)
        {
            System.out.println(e.getMessage());
            keyboardIn.next();
        }
    }
}