为什么不满足条件后我的 Do While 循环不停止？答案

【问题标题】：Why doesn't my Do While loop stop after the condition is not met?为什么不满足条件后我的 Do While 循环不停止？
【发布时间】：2019-10-01 21:32:55
【问题描述】：

我编写了一个代码，它获取用户在开始日期和结束日期的输入，并检查它们是否有效。在下面的代码中，我有 2 个 do..while 循环。一个用于开始日期，另一个用于结束日期。当执行第一个循环并且不满足条件时，程序不会继续执行另一个 do while 循环。如果我能收到此问题的解决方案，将会很有帮助。

int year, startMonth, endMonth, startDay, endDay; 
    boolean checkStartDate = false, checkEndDate = false;
    Scanner input = new Scanner (System.in);

    //checking Start Date
    do
    {   
    checkStartDate = false;
    System.out.print("Enter the year: ");
    year = input.nextInt();
    System.out.print("Enter the start month: ");
    startMonth = input.nextInt();
    System.out.print("Enter the start day: ");
    startDay = input.nextInt(); 

        switch (startMonth) 
        {
          case 1:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }
          break;

          case 2:
       if(startDay <= 28)
        {
            checkStartDate = true;
        }
            break;

          case 3:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }

            break;

          case 4:
        if(startDay <= 30)
        {
            checkStartDate = true;
        }
            break;

          case 5:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }
            break;

          case 6:
        if(startDay <= 30)
        {
            checkStartDate = true;
        }
            break;

          case 7:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }
            break;

          case 8:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }
            break;

          case 9:
        if(startDay <= 30)
        {
            checkStartDate = true;
        }
            break;

          case 10:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }
            break;

          case 11:
        if(startDay <= 30)
        {
            checkStartDate = true;
        }
            break;

          case 12:
        if(startDay <= 31)
        {
            checkStartDate = true;
            return;     
        }
          default:
          checkStartDate = false;
          System.out.println("Try again and enter a valid date \n");
        }   
        checkStartDate = false;

    } while (checkStartDate = true);

    //checking End Date

    do
    {   
    checkEndDate = false;
    System.out.print("Enter the year: ");
    year = input.nextInt();
    System.out.print("Enter the start month: ");
    endMonth = input.nextInt();
    System.out.print("Enter the start day: ");
    endDay = input.nextInt(); 

        switch (endMonth) 
        {
          case 1:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }

        else
        {
            checkEndDate = false;
            System.out.println("Print a valid start day");
        }
          break;

          case 2:
       if(endDay <= 28)
        {
           checkEndDate = true;
        }
            break;

          case 3:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }

            break;

          case 4:
        if(endDay <= 30)
        {
            checkEndDate = true;
        }
            break;

          case 5:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }
            break;

          case 6:
        if(endDay <= 30)
        {
            checkEndDate = true;
        }
            break;

          case 7:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }
            break;

          case 8:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }
            break;

          case 9:
        if(endDay <= 30)
        {
            checkEndDate = true;
        }
            break;

          case 10:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }
            break;

          case 11:
        if(endDay <= 30)
        {
            checkEndDate = true;
        }
            break;

          case 12:
        if(endDay <= 31)
        {
            checkEndDate = true;
            return;
        }

          default:
            checkEndDate = false;
            System.out.println("Try again and enter a valid date \n");
        }   
        checkEndDate = false;

    } while (checkEndDate = true);

    System.out.println("correct ");

【问题讨论】：

请注意：一旦您完成这项工作并拥有完整、可运行的代码，您可以将其发布到Code Review，我们可以帮助您编写更简洁的代码（例如改进巨人switch es）。

标签： java switch-statement boolean do-while

【解决方案1】：

while (checkEndDate = true)

您正在分配 checkEndDate 为真，因此循环将始终重复。您可能的意思是：

while (checkEndDate == true)

这比较两个值。但既然你已经有了一个布尔值，你就不需要比较了：

while (checkEndDate)

请注意，您可以通过组合相似的案例来显着减少代码量。例如：

case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
    if(startDay <= 31)
    {
        checkStartDate = true;
    }
    break;

30 天的月份也一样。

您还应该编写一个checkDate() 方法，这样您就不会重复编写相同的代码。

【讨论】：

【解决方案2】：

您在每个 do while 循环的末尾添加了 checkStartDate= false & checkEndDate = false;。这不是必需的。

将 while 条件更新为 while (checkStartDate); 作为其布尔值的评估。

下面是工作代码

int year, startMonth, endMonth, startDay, endDay; 布尔 checkStartDate = 假，checkEndDate = 假；扫描器输入 = 新扫描器 (System.in);

    //checking Start Date
    do
    {   
    checkStartDate = false;
    System.out.print("Enter the year: ");
    year = input.nextInt();
    System.out.print("Enter the start month: ");
    startMonth = input.nextInt();
    System.out.print("Enter the start day: ");
    startDay = input.nextInt(); 

        switch (startMonth) 
        {
          case 1:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }
          break;

          case 2:
       if(startDay <= 28)
        {
            checkStartDate = true;
        }
            break;

          case 3:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }

            break;

          case 4:
        if(startDay <= 30)
        {
            checkStartDate = true;
        }
            break;

          case 5:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }
            break;

          case 6:
        if(startDay <= 30)
        {
            checkStartDate = true;
        }
            break;

          case 7:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }
            break;

          case 8:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }
            break;

          case 9:
        if(startDay <= 30)
        {
            checkStartDate = true;
        }
            break;

          case 10:
        if(startDay <= 31)
        {
            checkStartDate = true;
        }
            break;

          case 11:
        if(startDay <= 30)
        {
            checkStartDate = true;
        }
            break;

          case 12:
        if(startDay <= 31)
        {
            checkStartDate = true;
            return;     
        }
          default:
          checkStartDate = false;
          System.out.println("Try again and enter a valid date \n");
        }   
       // checkStartDate = false;

    } while (checkStartDate);

    //checking End Date

    do
    {   
    checkEndDate = false;
    System.out.print("Check End Date... ");
    System.out.print("Enter the year: ");
    year = input.nextInt();
    System.out.print("Enter the start month: ");
    endMonth = input.nextInt();
    System.out.print("Enter the start day: ");
    endDay = input.nextInt(); 

        switch (endMonth) 
        {
          case 1:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }

        else
        {
            checkEndDate = false;
            System.out.println("Print a valid start day");
        }
          break;

          case 2:
       if(endDay <= 28)
        {
           checkEndDate = true;
        }
            break;

          case 3:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }

            break;

          case 4:
        if(endDay <= 30)
        {
            checkEndDate = true;
        }
            break;

          case 5:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }
            break;

          case 6:
        if(endDay <= 30)
        {
            checkEndDate = true;
        }
            break;

          case 7:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }
            break;

          case 8:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }
            break;

          case 9:
        if(endDay <= 30)
        {
            checkEndDate = true;
        }
            break;

          case 10:
        if(endDay <= 31)
        {
            checkEndDate = true;
        }
            break;

          case 11:
        if(endDay <= 30)
        {
            checkEndDate = true;
        }
            break;

          case 12:
        if(endDay <= 31)
        {
            checkEndDate = true;
            return;
        }

          default:
            checkEndDate = false;
            System.out.println("Try again and enter a valid date \n");
        }   
      //  checkEndDate = false; 

    } while (checkEndDate);

    System.out.println("correct ");

【讨论】：